mvebu: add specific signature support to Build/boot-scr

Add image-specific signature support to Build/boot-scr.
This is required to switch root devices passed to the kernel on Check
Point V-80 and V-81.

Signed-off-by: INAGAKI Hiroshi <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/16904
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/mvebu/image/Makefile

@@ -14,7 +14,7 @@ KERNEL_LOADADDR := 0x00008000
 define Build/boot-scr
 	rm -f [email protected]
 	sed \
-		-e 's#@ROOT@#$(IMG_PART_SIGNATURE)#g' \
+		-e 's#@ROOT@#$(if $(1),$(1),$(IMG_PART_SIGNATURE))#g' \
 		-e 's#@DTB@#$(firstword $(DEVICE_DTS))#g' \
 		$(BOOT_SCRIPT).bootscript > [email protected]
 	mkimage -A arm -O linux -T script -C none -a 0 -e 0 -d [email protected] [email protected]