build: centralize fakeroot code

This patch moves the fakeroot code required by some devices to
`image-commands.mk`.

Create the fakeroot on the fly by using the undocumented -s (skip copy)
parameter of mkimage.

Signed-off-by: Joseph C. Lehner <joseph.c.lehner@gmail.com>
[remove unused NETGEAR_KERNEL_MAGIC, remove workarounds to have a dummy
rootfs for mkimage]
Signed-off-by: Mathias Kresin <dev@kresin.me>

include/image-commands.mk

@@ -62,6 +62,18 @@ define Build/netgear-dni
 	mv $@.new $@
 endef
 
+# append a fake/empty rootfs uImage header, to fool the bootloaders
+# rootfs integrity check
+define Build/append-uImage-fakeroot-hdr
+	rm -f $@.fakeroot
+	$(STAGING_DIR_HOST)/bin/mkimage \
+		-A $(LINUX_KARCH) -O linux -T filesystem -C none \
+		-n '$(call toupper,$(LINUX_KARCH)) LEDE fakeroot' \
+		-s \
+		$@.fakeroot
+	cat $@.fakeroot >> $@
+endef
+
 define Build/tplink-safeloader
        -$(STAGING_DIR_HOST)/bin/tplink-safeloader \
 		-B $(TPLINK_BOARD_NAME) \
@@ -143,10 +155,6 @@ define Build/append-rootfs
 	dd if=$(IMAGE_ROOTFS) >> $@
 endef
 
-define Build/append-file
-	cat "$(1)" >> "$@"
-endef
-
 define Build/append-ubi
 	sh $(TOPDIR)/scripts/ubinize-image.sh \
 		$(if $(UBOOTENV_IN_UBI),--uboot-env) \