Makefile: add dtbs to clean

CI test checks that generated dtb has to be cleaned up.
Use the same clean procedure as Linux top level Makefile has.

Signed-off-by: Maxim Uvarov <maxim.uvarov@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/Makefile b/Makefile
index 220411a..b443831 100644
--- a/Makefile
+++ b/Makefile
@@ -2195,6 +2195,8 @@
 	@find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
 		\( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \
 		-o -name '*.ko.*' -o -name '*.su' -o -name '*.pyc' \
+		-o -name '*.dtb' -o -name '*.dtbo' \
+		-o -name '*.dtb.S' -o -name '*.dtbo.S' \
 		-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
 		-o -name '*.lex.c' -o -name '*.tab.[ch]' \
 		-o -name '*.asn1.[ch]' \