Debian: make sure osmo-bsc_mgcp ends up in its own package

... rather than being in the osmo-mgw package, which is clearly wrong.

Change-Id: Ib5d19f56b611722101040639db615184fa223f82
diff --git a/debian/osmo-bsc-mgcp.install b/debian/osmo-bsc-mgcp.install
new file mode 100644
index 0000000..1550437
--- /dev/null
+++ b/debian/osmo-bsc-mgcp.install
@@ -0,0 +1 @@
+usr/bin/osmo-bsc_mgcp