drm/i915: restore only the mode of this driver on lastclose (v2)

i915 calls the panic handler function on last close to reset the modes,
however this is a really bad idea for multi-gpu machines, esp shareable
gpus machines. So add a new entry point for the driver to just restore
its own fbcon mode.

v2: move code into fb helper, fix panic code to block mode change on
powered off GPUs.

[airlied: this hits drm core and I wrote it and it was reviewed on intel-gfx
 so really I signed it off twice ;-).]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/i915/intel_fb.c b/drivers/gpu/drm/i915/intel_fb.c
index 5127827..ec49bae 100644
--- a/drivers/gpu/drm/i915/intel_fb.c
+++ b/drivers/gpu/drm/i915/intel_fb.c
@@ -264,3 +264,13 @@
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	drm_fb_helper_hotplug_event(&dev_priv->fbdev->helper);
 }
+
+void intel_fb_restore_mode(struct drm_device *dev)
+{
+	int ret;
+	drm_i915_private_t *dev_priv = dev->dev_private;
+
+	ret = drm_fb_helper_restore_fbdev_mode(&dev_priv->fbdev->helper);
+	if (ret)
+		DRM_DEBUG("failed to restore crtc mode\n");
+}