ath9k: Separate routines for PCOEM and SoC calibration

Though there is some overlap between the calibration mechanisms
of PC-OEM cards and SoC chip families, dumping both of them
into a single function makes things hard to understand.

ar9003_hw_init_cal() is unreadable with chip-specific segments
scattered around. To make the logic understandable, use
different functions for client cards and SoC chips. Some
code is duplicated, but in the long run, it makes the code
more maintanable.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>