ARM: Align image end to 8 bytes to fit DT alignment

ARM: Align image end to 8 bytes to fit DT alignment

Align U-Boot image end to 8 bytes to make sure DT alignment requirement
is fulfilled. This fixes a possible failure in fdt_find_separate() in
case the U-Boot image is aligned to 4 Bytes and DT is appended at the
end at already 8 Byte aligned offset.

Link: https://source.denx.de/u-boot/u-boot/-/issues/30
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Marek Vasut <marek.vasut@mailbox.org>