ath9k: Add a HW capability for WLAN/BT RX diversity

Make use of this capability to restrict the usage of the
debugfs file and modparam using which this feature can
be enabled.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
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 fd009e5..4ab8f58 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -248,6 +248,7 @@
 	ATH9K_HW_WOW_DEVICE_CAPABLE		= BIT(17),
 	ATH9K_HW_CAP_PAPRD			= BIT(18),
 	ATH9K_HW_CAP_FCC_BAND_SWITCH		= BIT(19),
+	ATH9K_HW_CAP_BT_ANT_DIV			= BIT(20),
 };
 
 /*