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

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

Add multiple include guards.

APM was calling the suspend process from a timeout. This meant that
other timeouts could not happen while suspending, including timeouts
for things like msleep. This caused the system to hang on suspend
when the cbb was enabled, since its suspend path powered down the
socket which used a timeout to wait for it to be done.

APM now creates a thread when it is enabled, and deletes the thread
when it is disabled. This thread takes the place of the timeout by
doing its polling every ~.9s. When the thread is disabled, it will
wakeup early, otherwise it times out and polls the varius things the
old timeout polled (APM events, suspend delays, etc).

This makes my Sony VAIO 505TS suspend/resume correctly when APM is
enabled (ACPI is black listed on my 505TS).

This will likely fix other problems with the suspend path where
drivers would sleep with msleep and/or do other timeouts. Maybe
there's some special case code that would use DELAY while suspending
and msleep otherwise that can be revisited and removed.

This was also tested by glebius@, who pointed out that in the patch I
sent him, I'd forgotten apm_saver.c

MFC After: 3 weeks

/* -> /*- for copyright notices, minor format tweaks as necessary

o Return ai_batteries as 0xffffffff instead of -1. This is a nop change, but
placates gcc which seems to like to complain about -1 being assigned to
an unsigned value. It is well defined and intended, but since signess bugs
are being hunted just change to 0xffffffff.
o Mask the lower 8 bits, not the lower 4 bits for the ai_capabilities word.
All 8 bits are defined and the 0xf was almost certainly a typo.
o Define APM_UNKNOWN to 0xff for emulation layer.

Merge PC98 support.

Add Timer device driver for power management events.
The code for suspend/resume is derived from APM device driver.

Some people suggested the original code is somewhat buggy, but I'd
like to just move it from apm.c without any major changes for the
initial version. This code should be refined later.

To use pmtimer to adjust time at resume time, add
device pmtimer
in your kernel config file, and add
hint.pmtimer.0.at="isa"
in your device.hints

Reviewed by: -current, bde

Prepare for the apm_saver screen saver module.

1. Break out the definition of the soft state structure into an include
file.

2. un-static the soft state and apm_display(), and group them under a
comment that notes the dependency.