osmocom: Introduce META_TELEPHONY_OSMO_INC to easily bump version

For libosmocore updates we need a nice way to rebuild all libraries
using it. This can be done using the META_TELEPHONY_OSMO_INC variable.
diff --git a/recipes-osmocom/libosmo-sccp/libosmo-sccp.inc b/recipes-osmocom/libosmo-sccp/libosmo-sccp.inc
index 6c9d8e2..0a8e663 100644
--- a/recipes-osmocom/libosmo-sccp/libosmo-sccp.inc
+++ b/recipes-osmocom/libosmo-sccp/libosmo-sccp.inc
@@ -3,7 +3,7 @@
 HOMEPAGE = "http://openbsc.gnumonks.org"
 LICENSE = "GPL"
 
-INC_PR="r1"
+INC_PR="r1.${META_TELEPHONY_OSMO_INC}"
 
 LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"