add crcXXgen.c.tpl to EXTRA_DIST

'make distcheck' distributes the generated .c files, but it is good GPL
practice to also distribute the template.

Change-Id: I988acd3bc629e98985a99780d3142112125d13f7
diff --git a/src/Makefile.am b/src/Makefile.am
index 34cda0f..16119d9 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -49,7 +49,7 @@
 endif
 
 BUILT_SOURCES = crc8gen.c crc16gen.c crc32gen.c crc64gen.c
-EXTRA_DIST = conv_acc_sse_impl.h
+EXTRA_DIST = conv_acc_sse_impl.h crcXXgen.c.tpl
 
 libosmocore_la_LDFLAGS = -version-info $(LIBVERSION) -no-undefined