include: reorganize headers file to include/osmocom/[gsm|core]

This patch moves all GSM-specific definitions to include/osmocom/gsm.
Moreover, the headers in include/osmocore/ have been moved to
include/osmocom/core.

This has been proposed by Harald Welte and Sylvain Munaunt.

Tested with `make distcheck'.

Signed-off-by: Pablo Neira Ayuso <pablo@gnumonks.org>
diff --git a/include/Makefile.am b/include/Makefile.am
index 185c696..3578a80 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -1 +1 @@
-SUBDIRS = osmocom osmocore
+SUBDIRS = osmocom