drm/i915: The sprite scaler on Ironlake also support YUV planes

This fixes a regression from

commit 57779d06367a915ee03e6cb918d7575f0a46e419
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Wed Oct 31 17:50:14 2012 +0200

    drm/i915: Fix display pixel format handling

(which even says that they are supported on Ironlake, and then promptly
rejects then...)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -8637,7 +8637,7 @@ int intel_framebuffer_init(struct drm_device *dev,
 	case DRM_FORMAT_UYVY:
 	case DRM_FORMAT_YVYU:
 	case DRM_FORMAT_VYUY:
-		if (INTEL_INFO(dev)->gen < 6)
+		if (INTEL_INFO(dev)->gen < 5)
 			return -EINVAL;
 		break;
 	default: