Bluetooth: Controller: Make it possible to support only TX or RX DF

Some controllers may support only TXing or RXing CTE.
As all DF features are guarded by BT_CTLR_DF, we need to ensure
that it is possible to select those when only TX or RX is available.

Signed-off-by: Rubin Gerritsen <rubin.gerritsen@nordicsemi.no>
diff --git a/subsys/bluetooth/controller/Kconfig.df b/subsys/bluetooth/controller/Kconfig.df
index 733f7ac..9a7969c 100644
--- a/subsys/bluetooth/controller/Kconfig.df
+++ b/subsys/bluetooth/controller/Kconfig.df
@@ -35,7 +35,7 @@
 
 menuconfig BT_CTLR_DF
 	bool "LE Direction Finding [EXPERIMENTAL]"
-	depends on BT_CTLR_DF_SUPPORT
+	depends on BT_CTLR_DF_CTE_TX_SUPPORT || BT_CTLR_DF_CTE_RX_SUPPORT
 	select EXPERIMENTAL
 	help
 	  Enable support for Bluetooth 5.1 Direction Finding