image.mk: add support for specifying the VID header offset for UBI

Signed-off-by: Felix Fietkau <nbd@nbd.name>

include/image-commands.mk

@@ -107,6 +107,7 @@ define Build/append-ubi
 		$@.tmp \
 		-p $(BLOCKSIZE) -m $(PAGESIZE) \
 		$(if $(SUBPAGESIZE),-s $(SUBPAGESIZE)) \
+		$(if $(VID_HDR_OFFSET),-O $(VID_HDR_OFFSET)) \
 		$(UBINIZE_OPTS)
 	cat $@.tmp >> $@
 	rm $@.tmp

include/image.mk

@@ -295,6 +295,7 @@ define Device/Init
   BLOCKSIZE :=
   PAGESIZE :=
   SUBPAGESIZE :=
+  VID_HDR_OFFSET :=
   UBINIZE_OPTS := -E 5
   MKUBIFS_OPTS :=
 
@@ -310,7 +311,7 @@ DEFAULT_DEVICE_VARS := \
   DEVICE_NAME KERNEL KERNEL_INITRAMFS KERNEL_INITRAMFS_IMAGE \
   DEVICE_DTS DEVICE_DTS_DIR \
   UBOOTENV_IN_UBI KERNEL_IN_UBI \
-  BLOCKSIZE PAGESIZE SUBPAGESIZE \
+  BLOCKSIZE PAGESIZE SUBPAGESIZE VID_HDR_OFFSET \
   UBINIZE_OPTS
 
 define Device/ExportVar