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/src/gsm/Makefile.am b/src/gsm/Makefile.am
index a8c2e56..57eb5ca 100644
--- a/src/gsm/Makefile.am
+++ b/src/gsm/Makefile.am
@@ -7,7 +7,7 @@
 
 lib_LTLIBRARIES = libosmogsm.la
 
-libosmogsm_la_SOURCES = rxlev_stat.c tlv_parser.c comp128.c gsm_utils.c \
+libosmogsm_la_SOURCES = a5.c rxlev_stat.c tlv_parser.c comp128.c gsm_utils.c \
                         rsl.c gsm48.c gsm48_ie.c gsm0808.c \
 			gprs_cipher_core.c gsm0480.c
 libosmogsm_la_LIBADD = $(top_builddir)/src/libosmocore.la