Redirect checkpatch.sh to ../optee_os

use the checkpatch-helper scripts from optee_os repo

Signed-off-by: Markus S. Wamser <markus.wamser@mixed-mode.de>
Acked-by: Jerome Forissier <jerome@forissier.org>
diff --git a/Makefile b/Makefile
index 7a0018a..c186d91 100644
--- a/Makefile
+++ b/Makefile
@@ -210,6 +210,15 @@
 	$(q) echo "Please define CFG_GP_PACKAGE_PATH" && false
 endif
 
+.PHONY: checkpatch checkpatch-staging checkpatch-working
+checkpatch: checkpatch-staging checkpatch-working
+
+checkpatch-working:
+	@./scripts/checkpatch.sh
+
+checkpatch-staging:
+	@./scripts/checkpatch.sh --cached
+
 install:
 	$(echo) '  INSTALL ${DESTDIR}/lib/optee_armtz'
 	$(q)mkdir -p ${DESTDIR}/lib/optee_armtz