x86: fsp: Set up an MTRR for the graphics frame buffer

The FSP-S may do this but at least for coral it does not. Set this up so
that graphics is not deathly slow.

It isn't clear whether the FSP is expected to set up MTRR. It is not
mentioned in the APL FSP document.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>

arch/x86/lib/fsp/fsp_graphics.c

@@ -8,6 +8,7 @@
 #include <vbe.h>
 #include <video.h>
 #include <asm/fsp/fsp_support.h>
+#include <asm/mtrr.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -97,6 +98,9 @@ static int fsp_video_probe(struct udevice *dev)
 	if (ret)
 		goto err;
 
+	mtrr_add_request(MTRR_TYPE_WRCOMB, vesa->phys_base_ptr, 256 << 20);
+	mtrr_commit(true);
+
 	printf("%dx%dx%d\n", uc_priv->xsize, uc_priv->ysize,
 	       vesa->bits_per_pixel);