Bluetooth: controller: Add Kconfig option to enable debugging code in DF

To avid enabling HCI drived debugging, like in other controller source
files, Direction Finding has its own option BT_CTLR_DF_DEBUG_ENABLE.
This gives fine grained control deubgging output.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>
diff --git a/subsys/bluetooth/controller/Kconfig.df b/subsys/bluetooth/controller/Kconfig.df
index 98cf808..4b19d06 100644
--- a/subsys/bluetooth/controller/Kconfig.df
+++ b/subsys/bluetooth/controller/Kconfig.df
@@ -130,4 +130,10 @@
 	  In such case application is responsible for appropriate GPIOs
 	  initialization.
 
+config BT_CTLR_DF_DEBUG_ENABLE
+	bool "Bluetooth Direction Finding debug support enable"
+	help
+	  This option enables debug support for the Direction Finding
+	  implementation in controller.
+
 endif # BT_CTLR_DF