ath9k: add an interface for overriding the value of specific GPIO pins

Some devices control antenna settings or other things through GPIO pins
of the wireless interface. Add a debugfs interface for changing those
and keeping them set across card resets.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/hw.h b/drivers/net/wireless/ath/ath9k/hw.h
index c86eea2..775c0eb 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -799,6 +799,8 @@
 	int initPDADC;
 	int PDADCdelta;
 	u8 led_pin;
+	u32 gpio_mask;
+	u32 gpio_val;
 
 	struct ar5416IniArray iniModes;
 	struct ar5416IniArray iniCommon;