ath9k_hw: add GPIO setup code for AR9271

Assign the proper number of GPIO pins for AR9271.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>