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/tests/mgcp/mgcp_transcoding_test.c b/openbsc/tests/mgcp/mgcp_transcoding_test.c
index e5da138..9ba2c4b 100644
--- a/openbsc/tests/mgcp/mgcp_transcoding_test.c
+++ b/openbsc/tests/mgcp/mgcp_transcoding_test.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"
 
 uint8_t *audio_frame_l16[] = {
 };