bsc: Move the osmo_bsc_rf file into the libbsc code and rename

The nitb will provide the RF interface as well.
diff --git a/openbsc/src/libbsc/Makefile.am b/openbsc/src/libbsc/Makefile.am
index 4cf1fab..6f170e0 100644
--- a/openbsc/src/libbsc/Makefile.am
+++ b/openbsc/src/libbsc/Makefile.am
@@ -21,5 +21,5 @@
 			e1_config.c \
 			bsc_api.c bsc_msc.c bsc_vty.c \
 			gsm_04_08_utils.c \
-			bsc_init.c bts_init.c
+			bsc_init.c bts_init.c bsc_rf_ctrl.c