ath9k: add power per-rate tables for AR9002 chips

Add TX power per-rate tables for MIMO/legacy modes for AR9002 based chips
in order to cap the maximum TX power value per-rate in the TX descriptor path.
Add TX power adjustments for HT40 mode, open loop CCK rates and eeprom power
bias for AR9280 and later chips

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>