efifb: BGRT: Add nobgrt option

In some setups restoring the BGRT logo is undesirable, allow passing
video=efifb:nobgrt on the kernel commandline to disable it.

Reported-by: David Herrmann <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>
Reviewed-by: David Herrmann <[e-mail]>
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>

drivers/video/fbdev/efifb.c

···
 	u32 colors_important;
 } __packed;
 
+static bool use_bgrt = true;
 static bool request_mem_succeeded = false;
 static u64 mem_flags = EFI_MEMORY_WC | EFI_MEMORY_UC;
 
···
 	struct bmp_dib_header *dib_header;
 	void *bgrt_image = NULL;
 	u8 *dst = info->screen_base;
+
+	if (!use_bgrt)
+		return;
 
 	if (!bgrt_tab.image_address) {
 		pr_info("efifb: No BGRT, not showing boot graphics\n");
···
 				screen_info.lfb_width = simple_strtoul(this_opt+6, NULL, 0);
 			else if (!strcmp(this_opt, "nowc"))
 				mem_flags &= ~EFI_MEMORY_WC;
+			else if (!strcmp(this_opt, "nobgrt"))
+				use_bgrt = false;
 		}
 	}