ath9k: Add new Atheros IEEE 802.11n driver

This adds the new mac80211 11n ath9k Atheros driver. Only STA support
is currently enabled and tested.

Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Jack Howarth <howarth@bromo.msbb.uc.edu>
Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>