Add the following macro from the UEFI spec, for completeness:

  EFI_MEMORY_UCE  Memory cacheability attribute: The memory region
                  supports being configured as not cacheable, exported,
                  and supports the "fetch and add" semaphore mechanism.
Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Tested-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NMatt Fleming <matt.fleming@intel.com>