Installing UEFI configuration tables can only be done before calling
ExitBootServices(), so if we want to use the new MEMRESRVE config table
from the kernel proper, we need to install a dummy entry from the stub.
Tested-by: NJeremy Linton <jeremy.linton@arm.com>
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>