[ARM] pxa: fix overlay being un-necessarily initialized on pxa25x

pxa25x doesn't support overlay in its LCD controller, this patch adds
pxafb_overlay_supported() functions to check the initialization is
necessary.
Signed-off-by: NEric Miao <eric.miao@marvell.com>

drivers/video/pxafb.c

@@ -883,10 +883,21 @@ static void __devinit init_pxafb_overlay(struct pxafb_info *fbi,
 	init_completion(&ofb->branch_done);
 }
 
+static inline int pxafb_overlay_supported(void)
+{
+	if (cpu_is_pxa27x() || cpu_is_pxa3xx())
+		return 1;
+
+	return 0;
+}
+
 static int __devinit pxafb_overlay_init(struct pxafb_info *fbi)
 {
 	int i, ret;
 
+	if (!pxafb_overlay_supported())
+		return 0;
+
 	for (i = 0; i < 2; i++) {
 		init_pxafb_overlay(fbi, &fbi->overlay[i], i);
 		ret = register_framebuffer(&fbi->overlay[i].fb);
@@ -909,6 +920,9 @@ static void __devexit pxafb_overlay_exit(struct pxafb_info *fbi)
 {
 	int i;
 
+	if (!pxafb_overlay_supported())
+		return;
+
 	for (i = 0; i < 2; i++)
 		unregister_framebuffer(&fbi->overlay[i].fb);
 }