simplefb: use write-combined remapping

Framebuffers shouldn't be cached and it is usually very uncommon to read
them. Therefore, use ioremap_wc() to get significant speed improvements on
systems which provide it. On all other systems it's aliased to
ioremap_nocache() which is also fine.

Reported-by: Tom Gundersen <teg@jklm.no>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Tested-by: Tom Gundersen <teg@jklm.no>
Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/simplefb.c

@@ -219,7 +219,7 @@ static int simplefb_probe(struct platform_device *pdev)
 
 	info->fbops = &simplefb_ops;
 	info->flags = FBINFO_DEFAULT | FBINFO_MISC_FIRMWARE;
-	info->screen_base = ioremap(info->fix.smem_start,
+	info->screen_base = ioremap_wc(info->fix.smem_start,
 				       info->fix.smem_len);
 	if (!info->screen_base) {
 		framebuffer_release(info);