separate libosmo-mgcp-client from mgcp server code

When osmo-mgw is built --with-mgcp-transcoding, linking the mgcp library
also requires linking libgsm, even though e.g. osmo-msc never use it.
Separate the MGCP client code from the MGCP server code to avoid this dep.

The mgcp client code does use some definitions from mgcp.h and mgcp_common.c.
For simplicity, link mgcp_common.c in both libosmo-legacy-mgcp as well as
libosmo-mgcp-client. That means it is not possible to link both
libosmo-legacy-mgcp and libosmo-mgcp-client in the same binary because of
duplicate symbols, but currently that is sufficient. (An alternative would be
code dup or yet another libosmo-mgcp-common library.)

Add libosmo-mgcp-client to debian packaging.

Related: OS#2488
Change-Id: I8e0b2d2a399b77086a36606f5e427271c6242df1
diff --git a/Makefile.am b/Makefile.am
index c5c3137..8fb6e6c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -17,7 +17,10 @@
 	$(NULL)
 
 pkgconfigdir = $(libdir)/pkgconfig
-pkgconfig_DATA = libosmo-legacy-mgcp.pc
+pkgconfig_DATA = \
+	libosmo-legacy-mgcp.pc \
+	libosmo-mgcp-client.pc \
+	$(NULL)
 
 BUILT_SOURCES = $(top_srcdir)/.version
 EXTRA_DIST = git-version-gen osmoappdesc.py .version