SDK: make sure to include libosmo-abis, libdbi and libgtp headers

This enables the SDK to do a full openbsc build.
diff --git a/recipes-osmocom/tasks/task-sdk-osmo.inc b/recipes-osmocom/tasks/task-sdk-osmo.inc
index 45c37c7..0eac22a 100644
--- a/recipes-osmocom/tasks/task-sdk-osmo.inc
+++ b/recipes-osmocom/tasks/task-sdk-osmo.inc
@@ -1,6 +1,9 @@
 SDK-OSMO = " \
     libosmocore-dev \
     libosmo-sccp-dev \
+    libosmo-abis-dev \
+    libgtp-dev \
+    libdbi-dev \
     "
 
 SDK-EXTRAS ?= ""