Move vlr.h & vlr_sgs.h into osmocom/vlr/

Prepare libvlr to be independent, start by moving the vlr headers
into its own directory.

Change-Id: I8b18b05091b35e744b3234d1ce0d537f56bccf07
diff --git a/src/libmsc/msc_ho.c b/src/libmsc/msc_ho.c
index cea658c..d5dba30 100644
--- a/src/libmsc/msc_ho.c
+++ b/src/libmsc/msc_ho.c
@@ -34,7 +34,7 @@
 #include <osmocom/msc/neighbor_ident.h>
 #include <osmocom/msc/gsm_data.h>
 #include <osmocom/msc/ran_peer.h>
-#include <osmocom/msc/vlr.h>
+#include <osmocom/vlr/vlr.h>
 #include <osmocom/msc/transaction.h>
 #include <osmocom/msc/gsm_04_08.h>
 #include <osmocom/msc/call_leg.h>