efi: avoid error message when booting under Xen

efifb_probe() will issue an error message in case the kernel is booted
as Xen dom0 from UEFI as EFI_MEMMAP won't be set in this case. Avoid
that message by calling efi_mem_desc_lookup() only if EFI_MEMMAP is set.

Fixes: 38ac0287b7 ("fbdev/efifb: Honour UEFI memory map attributes when mapping the FB")
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/video/fbdev/efifb.c

@@ -453,7 +453,7 @@ static int efifb_probe(struct platform_device *dev)
 	info->apertures->ranges[0].base = efifb_fix.smem_start;
 	info->apertures->ranges[0].size = size_remap;
 
-	if (efi_enabled(EFI_BOOT) &&
+	if (efi_enabled(EFI_MEMMAP) &&
 	    !efi_mem_desc_lookup(efifb_fix.smem_start, &md)) {
 		if ((efifb_fix.smem_start + efifb_fix.smem_len) >
 		    (md.phys_addr + (md.num_pages << EFI_PAGE_SHIFT))) {