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

MFC 264019, 264041, 264048, 264049, 264050, 264051

Add support for event timers whose clock frequency can change while running.

Apparently all ARM configs build kern_et.c, but only a few of them also
build kern_clocksource.c, un-break the build by not referencing functions in
kern_clocksource if NO_EVENTTIMERS is defined.

Add variable-frequency support to the arm mpcore eventtimer driver.

mpcore_timer: Disable the timer and clear any pending bit, then setup the
new counter register values, then restart the timer. Also re-nest the parens
properly for casting the result of converting time and frequency to a count.

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

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

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.

mdoc(7) markup cleanup.

Remove trailing whitespace per mdoc lint warning

Disussed with: gavin
No objection from: doc
Approved by: joel
MFC after: 3 days

Globally replace u_int*_t from (non-contributed) man pages.

The reasoning behind this, is that if we are consistent in our
documentation about the uint*_t stuff, people will be less tempted to
write new code that uses the non-standard types.

I am not going to bump the man page dates, as these changes can be
considered style nits. The meaning of the man pages is unaffected.

MFC after: 1 month

Add eventtimers(9) man page, describing related KPIs.

Sponsored by: iXsystems, Inc.
MFC after: 1 month