gsm/a5: Add a A5 1&2 implementation

It's always useful to have around

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/gsm/Makefile.am b/include/osmocom/gsm/Makefile.am
index 8685fc9..a39d2d0 100644
--- a/include/osmocom/gsm/Makefile.am
+++ b/include/osmocom/gsm/Makefile.am
@@ -1,4 +1,4 @@
-osmogsm_HEADERS = comp128.h gsm0808.h gsm48_ie.h mncc.h rxlev_stat.h \
+osmogsm_HEADERS = a5.h comp128.h gsm0808.h gsm48_ie.h mncc.h rxlev_stat.h \
 		  gsm0480.h gsm48.h gsm_utils.h rsl.h tlv.h
 
 SUBDIRS = protocol