efi: Add macro for EFI_MEMORY_UCE memory attribute

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: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

include/linux/efi.h

@@ -92,6 +92,7 @@ typedef	struct {
 #define EFI_MEMORY_WC		((u64)0x0000000000000002ULL)	/* write-coalescing */
 #define EFI_MEMORY_WT		((u64)0x0000000000000004ULL)	/* write-through */
 #define EFI_MEMORY_WB		((u64)0x0000000000000008ULL)	/* write-back */
+#define EFI_MEMORY_UCE		((u64)0x0000000000000010ULL)	/* uncached, exported */
 #define EFI_MEMORY_WP		((u64)0x0000000000001000ULL)	/* write-protect */
 #define EFI_MEMORY_RP		((u64)0x0000000000002000ULL)	/* read-protect */
 #define EFI_MEMORY_XP		((u64)0x0000000000004000ULL)	/* execute-protect */