arc770: gzip rootfs image to save some space

Signed-off-by: Felix Fietkau <[email protected]>

target/linux/arc770/image/Makefile

@@ -81,6 +81,7 @@ define Image/Build
 	$(call Image/Build/$(1),$(1))
 	$(call Image/Build/SDCard,$(1))
 	dd if=$(KDIR)/root.$(1) of=$(BIN_DIR)/$(IMG_PREFIX)-root.$(1) bs=128k conv=sync
+	$(call Image/Gzip,$(BIN_DIR)/$(IMG_PREFIX)-root.$(1))
 endef
 
 $(eval $(call BuildImage))