layerscape: add dtb to sysupgrade

layerscape: add dtb to sysupgrade

At this moment sysupgrade replaces only kernel and rootfs.

This patch add dtb part to sysupgrade images to avoid situation
when old dtb make system broken.

Is possible to sysupgrade older images for NOR devices:
1. Firmware partition in bootargs need to be updated to:
   "49m@0xf00000(firmware)". Env should be saved after changes.
2. After step one, "sysupgrade -F" will work.

Run tested: LS1046A-RDB

Reviewed-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
[bump PKG_RELEASE for uboot-layerscape]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>