Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Cleanup and document the implementation of firmware(9) based on
a version that i posted earlier on the -current mailing list,
and subsequent feedback received.

The core of the change is just in sys/firmware.h and kern/subr_firmware.c,
while other files are just adaptation of the clients to the ABI change
(const-ification of some parameters and hiding of internal info,
so this is fully compatible at the binary level).

In detail:
- reduce the amount of information exported to clients in struct firmware,
and constify the pointer;

- internally, document and simplify the implementation of the various
functions, and make sure error conditions are dealt with properly.

The diffs are large, but the code is really straightforward now (i hope).

Note also that there is a subtle issue with the implementation of
firmware_register(): currently, as in the previous version, we just
store a reference to the 'imagename' argument, but we should rather
copy it because there is no guarantee that this is a static string.
I realised this while testing this code, but i prefer to fix it in
a later commit -- there is no regression with respect to the past.

Note, too, that the version in RELENG_6 has various bugs including
missing locks around the module release calls, mishandling of modules
loaded by /boot/loader, and so on, so an MFC is absolutely necessary
there. I was just postponing it until this cleanup to avoid doing
things twice.

MFC after: 1 week

Move the new flags field to the end of the structure to maintain
ABI compatibility.

Suggested by: mlaier (and forgotten by me)

Keep firmware images on the list until they have been unregistered
with firmware_unregister(). Previously when the last driver reference
had been dropped we would clear the list entry under the assumption
that the firmware module was about to be unloaded, but this was not
true if the firmware image had been loaded manually with kldload.

This makes it possible to manually kldload firmware images as a
workaround for drivers such as ipw that attempt to load firmware
while resuming after a suspend.

Reviewed by: mlaier (an earlier version of the patch)

firmware(9) is a subsystem to load binary data into the kernel via a
specially crafted module. There are several handrolled sollutions to this
problem in the tree already which will be replaced with this. They include
iwi(4), ipw(4), ispfw(4) and digi(4).

No objection from: arch
MFC after: 2 weeks
X-MFC after: some drivers have been converted