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/contrib/testconv/testconv_main.c b/openbsc/contrib/testconv/testconv_main.c
index e74c686..89dce1a 100644
--- a/openbsc/contrib/testconv/testconv_main.c
+++ b/openbsc/contrib/testconv/testconv_main.c
@@ -17,7 +17,7 @@
 #error "Requires MGCP transcoding enabled (see --enable-mgcp-transcoding)"
 #endif
 
-#include "src/osmo-bsc_mgcp/mgcp_transcode.h"
+#include "openbsc/mgcp_transcode.h"
 
 static int audio_name_to_type(const char *name)
 {