mgcp: Move transcoding to libmgcp

This patch moves the files relevant to transcoding from
src/osmo-bsc_mgcp to src/libmgcp and src/include/openbsc. Makefiles
and include directives are being updated accordingly.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/osmo-bsc_mgcp/mgcp_main.c b/openbsc/src/osmo-bsc_mgcp/mgcp_main.c
index 6b72965..8c3808a 100644
--- a/openbsc/src/osmo-bsc_mgcp/mgcp_main.c
+++ b/openbsc/src/osmo-bsc_mgcp/mgcp_main.c
@@ -50,7 +50,7 @@
 #include "../../bscconfig.h"
 
 #ifdef BUILD_MGCP_TRANSCODING
-#include "mgcp_transcode.h"
+#include "openbsc/mgcp_transcode.h"
 #endif
 
 /* this is here for the vty... it will never be called */