ath5k: Update channel functions

 * Add channel function for RF2425 (got this from decompiling binary
   HAL, i have no idea why there is a 5GHz section but i'm looking
   into it)
 * Update RF5112 channel function (also got this from decompiling binary HAL)
 * Set JAPAN setting for channel 14 on all PHY chips

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