drm/i915: Disable FBC if BIOS reserved memory (stolen) is unavailable

The FBC requires a couple of contiguous buffers, which we allocate from
stolen memory. If stolen memory is unavailable, we cannot allocate those
buffers and so cannot support FBC. Mark it so.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190911175926.31365-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/display/intel_fbc.c

@@ -1320,6 +1320,9 @@ void intel_fbc_init(struct drm_i915_private *dev_priv)
 	fbc->enabled = false;
 	fbc->active = false;
 
+	if (!drm_mm_initialized(&dev_priv->mm.stolen))
+		mkwrite_device_info(dev_priv)->display.has_fbc = false;
+
 	if (need_fbc_vtd_wa(dev_priv))
 		mkwrite_device_info(dev_priv)->display.has_fbc = false;