ath9k: Split ath9k_hw_btcoex_enable() into two logical pieces

This function currently does initialization + enable the
btcoex support. Split it into two logical functions which
does the above operations separately. Btcoex initialization
is done during attach time and enabling this feature is done
in start(). Also, add code to disable btcoex support in stop().

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/ath9k.h b/drivers/net/wireless/ath/ath9k/ath9k.h
index 7705da1..0868800 100644
--- a/drivers/net/wireless/ath/ath9k/ath9k.h
+++ b/drivers/net/wireless/ath/ath9k/ath9k.h
@@ -521,6 +521,7 @@
 #define SC_OP_WAIT_FOR_PSPOLL_DATA BIT(17)
 #define SC_OP_WAIT_FOR_TX_ACK   BIT(18)
 #define SC_OP_BEACON_SYNC       BIT(19)
+#define SC_OP_BTCOEX_ENABLED    BIT(20)
 
 struct ath_bus_ops {
 	void		(*read_cachesize)(struct ath_softc *sc, int *csz);