ath9k_hw: Add AR9003 PHY support

This add stubs for PHY support for the AR9003 hardware family.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>