make: add support for "mobile" from osmocom-bb

Allow building and installing the "mobile" application from
osmocom-bb.git's src/host/layer23 dir.

Change-Id: Ic75cca703e317eaee593b4d6c78784309c056f17
diff --git a/all.deps b/all.deps
index 20972a8..85b8d34 100644
--- a/all.deps
+++ b/all.deps
@@ -30,3 +30,7 @@
 # can only clone these
 docker-playground
 osmo-ttcn3-hacks
+osmocom-bb
+
+# configure.ac not in topdir of repository
+osmocom-bb_layer23	libosmocore