ath9k: move ath9k_init_channels_rates to common-init

and rename it to ath9k_cmn_init_channels_rates.
sbands are move to ath_common as well.

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>