Makefile: Add tags rule

It's useful to have some tags to jump around sources. We don't
include test sources in the toplevel Makefile because they
probably aren't useful to main program development.

Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Makefile

@@ -218,6 +218,12 @@ kup: dist
 		$(KUPDIR)/dtc-$(dtc_version).tar.gz
 endif
 
+tags: FORCE
+	rm -f tags
+	find . \( -name tests -type d -prune \) -o \
+	       \( ! -name '*.tab.[ch]' ! -name '*.lex.c' \
+	       -name '*.[chly]' -type f -print \) | xargs ctags -a
+
 #
 # Testsuite rules
 #