Port over the AR9285 PA calibration and initial calibration code from

Port over the AR9285 PA calibration and initial calibration code from
Linux ath9k.

The ath9k ar9002_hw_init_cal() isn't entirely clear about what
is supposed to be called for what chipsets, so I'm ignoring the
rest of it and just porting the AR9285 init cal path as-is and
leaving the rest alone. Subsequent commits may also tidy up the
Merlin (AR9285) and other chipset support.

Obtained from:	Linux ath9k