MFC r306436-r306437, r306489, r306491

r306436 by manu:
RPI-B: Add support for MULTIDELAY

100 cycles per us seems accurate enough, at least it's better than the 200 value
that was used before.

Reviewed by: andrew, imp
Differential Revision: https://reviews.freebsd.org/D8062

r306437 by manu:
RPI2: Add support for PLATFORM_SMP so we can later add it to GENERIC.

Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D8063

r306489 by manu:
bcm2835_cpufreq: Only attach driver if we correcly match on the machine
compatible string.

r306491 by manu:
RPI2: Add support for MULTIDELAY, this is needed for inclusion into GENERIC.

Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Use simple fixed name strings for these timecounters and eventimers which
are tied to fixed pieces of hardware; dynamic string formatting isn't needed.

Stop using machine/fdt.h in the arm kernel code when we don't need it.

Replace many pasted identical definitions of cpu_initclocks() with a common
implementation in arm/machdep.c. Most arm platforms either don't need to
do anything, or just need to call the standard eventtimer init routines.
A generic implementation that does that is now provided via weak linkage.
Any platform that needs to do something different can provide a its own
implementation to override the generic one.

Follow r261352 by updating all drivers which are children of simplebus
to check the status property in their probe routines.

Simplebus used to only instantiate its children whose status="okay"
but that was improper behavior, fixed in r261352. Now that it doesn't
check anymore and probes all its children; the children all have to
do the check because really only the children know how to properly
interpret their status property strings.

Right now all existing drivers only understand "okay" versus something-
that's-not-okay, so they all use the new ofw_bus_status_okay() helper.

Remove #include <machine/frame.h> from all the arm code that doesn't
really need it. That would be almost everywhere it was included. Add
it in a couple files that really do need it and were previously getting
it by accident via another header.

Fix DELAY() on RPi, the wrong math was making it take twice it should.

Reported by: Alexander <sht@ropnet.ru>
Approved by: adrian (mentor)
Approved by: re (gjb)

Minimal timer period of 100us introduced in r244758 is overkill. While
original 2us are indeed not enough, 3us are working quite well on my tests.
To be more safe set minimal period to 5us and to be even more safe replicate
here from HPET mechanism of rereading counter after programming comparator.

This change allows to handle 30K of short nanosleep() calls per second on
Raspberry Pi instead of just 8K before.

Discussed with: gonzo

MFcalloutng:
Switch eventtimers(9) from using struct bintime to sbintime_t.
Even before this not a single driver really supported full dynamic range of
struct bintime even in theory, not speaking about practical inexpediency.
This change legitimates the status quo and cleans up the code.

Fix event timer on Raspberry Pi

- Disable interrupt when updating compare value in order to
make this operation atomical

- Increase minimum period for event timer. Systimer on BCM2835
is compare timer, so if minimum period is too small it might
be less then fraction of time between "read current value" and
"set compare timer" operations. It means that when timer is armed
actual counter value is more then compare value and it will take
whole cycle (~32sec for 1MHz timer) to fire interrupt.

Submitted by: Daisuke Aoyama <aoyama at peach.ne.jp>

Fix spelling.

remove duplicate semicolons where possible.

Approved by: cperciva
MFC after: 1 week

Add barebone Raspberry Pi port. Supported parts:
- Interrupts controller
- Watchdog
- System timer
- Framebuffer (hardcoded resolution/bpp)