ath5k: Convert chip specific calibration data to a generic format

* Convert chip specific calibration data to a generic format common
for all chips

Note: We scale up power to be in 0.25dB units for all chips for
compatibility with RF5112

v2: Address Bob's and Jiri's comments

Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>