ath9k: Fix TX99 config option usage

Use CONFIG_ATH9K_TX99 to properly enclose the tx99 code
and make sure that it is not compiled as part of the driver
when it is not selected. Move the tx99 code to a new file tx99.c
and also add ATH9K_DEBUGFS as a dependency in Kconfig.

This reduces the module size on platforms like OpenWrt where
ATH9K_DEBUGFS is selected, but TX99 might be disabled.

Cc: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/xmit.c

@@ -2749,6 +2749,8 @@ void ath_tx_node_cleanup(struct ath_softc *sc, struct ath_node *an)
 	}
 }
 
+#ifdef CONFIG_ATH9K_TX99
+
 int ath9k_tx99_send(struct ath_softc *sc, struct sk_buff *skb,
 		    struct ath_tx_control *txctl)
 {
@@ -2791,3 +2793,5 @@ int ath9k_tx99_send(struct ath_softc *sc, struct sk_buff *skb,
 
 	return 0;
 }
+
+#endif /* CONFIG_ATH9K_TX99 */