Makefile: Add 'deps-update' target to update the deps-repository

Change-Id: Idc165425b45872d2eb958a662d03e69aaf60669d
diff --git a/Makefile b/Makefile
index f009560..8999ec8 100644
--- a/Makefile
+++ b/Makefile
@@ -20,6 +20,10 @@
 deps:
 	$(MAKE) -C deps
 
+.PHONY: deps-update
+deps-update:
+	$(MAKE) -C deps update
+
 compile: $(foreach dir,$(SUBDIRS),$(dir)/compile)
 clean: $(foreach dir,$(SUBDIRS),$(dir)/clean)
 all: $(foreach dir,$(SUBDIRS),$(dir)/all)