Add a <fs>-root-show-depends target

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

fs/common.mk

@@ -57,6 +57,9 @@ ifeq ($$(BR2_TARGET_ROOTFS_$(2)_LZMA),y)
 	$(LZMA) -9 -c $$@ > $$@.lzma
 endif
 
+$(1)-root-show-depends:
+	@echo $(ROOTFS_$(2)_DEPENDENCIES) host-fakeroot host-makedevs $(if $(BR2_TARGET_ROOTFS_$(2)_LZMA),host-lzma)
+
 $(1)-root: $(BINARIES_DIR)/rootfs.$(1)
 
 ifeq ($$(BR2_TARGET_ROOTFS_$(2)),y)