fdtdec: apply DT overlays from bloblist

fdtdec: apply DT overlays from bloblist

During FDT setup, apply all existing DT overlays from the bloblist
to the base FDT if bloblist is being used for handoff from previous
boot stage.
According to the Firmware Handoff spec update to support DT overlay [1],
an overlay must have the same top-level compatible string as its target
base DT has.
Before applying the overlays, check whether sufficient space is
reserved in the base DT blob, if not, resize the blob to the allowed
padded size, which is limited by CONFIG_SYS_FDT_PAD and the bloblist
spare space size.
After all overlays are applied, resize the merged DT to its actual size.

[1] Add Transfer Entry for Devicetree Overlay
https://github.com/FirmwareHandoff/firmware_handoff/pull/74

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Tested-by: Michal Simek <michal.simek@amd.com>