Similar as available for u-boot (ce2995e1dc)
and syslinux (c5112c25e4), enable parsing
and writing devicetree filename into grub.cfg.
This is required by arm64-based devices running edk2 instead of u-boot
as the main bootloader (e.g. 96boards HiKey and HiKey960).
Signed-off-by: Ricardo Salveti <ricardo@foundries.io>
Closes: #1790
Approved by: cgwalters