arm64/efi: ignore DT memreserve entries instead of removing them

arm64/efi: ignore DT memreserve entries instead of removing them

Now that the reservation of the FDT image itself is split off, we
can make the DT scanning of memreserves conditional on whether we
booted via UEFI and have its memory map available. This allows us
to drop deletion of these memreserves in the stub. It also fixes
the issue where the /reserved-memory/ node (which offers another
way of reserving memory ranges) was not being ignored under UEFI.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev@caviumnetworks.com>