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

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

Break out the PLL setup into (mostly) per-chip methods, rather than
polluting the AR5416 code with later chipset support.

Note: ar9280InitPLL() supports Merlin (AR9280) and later (AR9285, AR9287.)

Submitted by: ssgriffonuser@gmail.com
Approved by: re (kib)

Implement open-loop TX power control (OLC) for Merlin (AR9280) and
generally tidy up the TX power programming code.

Enforce that the TX power offset for Merlin is -5 dBm, rather than
any other value programmable in the EEPROM. This requires some
further code to be ported over from ath9k, so until that is done
and tested, fail to attach NICs whose TX power offset isn't -5
dBm.

This improves both legacy and HT transmission on my merlin board.
It allows for stable MCS TX up to MCS15.

Specifics:

* Refactor out a bunch of the TX power calibration code -
setting/obtaining the power detector / gain boundaries,
programming the PDADC
* Take the -5 dBm TX power offset into account on Merlin -
"0" in the per-rate TX power register means -5 dBm, not
0 dBm
* When doing OLC
* Enforce min (0) and max (AR5416_MAX_RATE_POWER) when fiddling
with the TX power, to avoid the TX power values from wrapping
when low.
* Implement the 1 dBm cck power offset when doing OLC
* Implement temperature compensation for 2.4ghz mode when doing OLC
* Implement an AR9280 specific TX power calibration routine which
includes the OLC twiddles, leaving the earlier chipset path
(AR5416, AR9160) alone

Whilst here, use these refactored routines for the AR9285 TX power
calibration/programming code and enforce correct overflow/underflow
handling when fiddling with TX power values.

Obtained from: linux ath9k

Bring over some NF calibration changes from ath9k.

Each different radio chipset has a different "good" range of CCA
(clear channel access) parameters where, if you write something
out of range, it's possible the radio will go deaf.

Also, since apparently occasionally reading the NF calibration
returns "wrong" values, so enforce those limits on what is being
written into the CCA register.

Write a default value if there's no history available.

This isn't the case right now but it may be later on when "off-channel"
scanning occurs without init'ing or changing the NF history buffer.
(As each channel may have a different noise floor; so scanning or
other off-channel activity shouldn't affect the NF history of
the current channel.)

Push the non-AR5416 related stuff into chipset specific directories.

sys/dev/ath/ath_hal/ar5416/ is getting very crowded and further
commits will make it even more crowded. Now is a good time to
shuffle these files out before any more extensive work is done
on them.

Create an ar9003 directory whilst I'm here; ar9003 specific
chipset code will eventually live there.

Bring back AR9285 support. This fixes most of the issues and should be
pretty usable.

MFC after: 1 month

Fix TX power problems with AR9285.

preliminary ar9280 support:
o add 9280 attach that sets up ini, cal, etc.
o new rf backend for 9280 and later parts
o split ini setup and spur mitigation support out to methods
and provide 9280-specific support
o minor fixups to shared code to handle 9280-specific work

Obtained from: Atheros (ini values and some code)