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/osmocom/Makefile.am b/include/osmocom/Makefile.am
index ec548fb..21f4f2d 100644
--- a/include/osmocom/Makefile.am
+++ b/include/osmocom/Makefile.am
@@ -1,5 +1,5 @@
 if ENABLE_VTY
-SUBDIRS = vty codec crypt
+SUBDIRS = vty codec crypt gsm core
 else
-SUBDIRS = codec crypt
+SUBDIRS = codec crypt gsm core
 endif