drm/i915: Fix FBC1 plane checks for gen2

On gen2 and gen3 chipsets FBC is supported only on plane A. Fix (and
simplify) the plane checks in intel_update_fbc() accordingly.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -537,10 +537,10 @@ void intel_update_fbc(struct drm_device *dev)
 			DRM_DEBUG_KMS("mode too large for compression, disabling\n");
 		goto out_disable;
 	}
-	if ((IS_I915GM(dev) || IS_I945GM(dev) || IS_HASWELL(dev)) &&
-	    intel_crtc->plane != 0) {
+	if ((INTEL_INFO(dev)->gen < 4 || IS_HASWELL(dev)) &&
+	    intel_crtc->plane != PLANE_A) {
 		if (set_no_fbc_reason(dev_priv, FBC_BAD_PLANE))
-			DRM_DEBUG_KMS("plane not 0, disabling compression\n");
+			DRM_DEBUG_KMS("plane not A, disabling compression\n");
 		goto out_disable;
 	}