ath9k_hw: Enable AR9340 support

AR9340 is a AR9003 family built-in 2x2 wmac of ar934x SOCs. It is single band
in ar9341 SOC and dual band in ar9344/ar9342 SOCs.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>