Implement a version of the NOR Flash driver that can execute in standalone MM context. This is used to access the secure variable storage, it only supports EFI_FIRMWARE_VOLUME_BLOCK2_PROTOCOL. Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>