drm: Add support for multiple plane types (v2)

The DRM core currently only tracks "overlay"-style planes.  Start
refactoring the plane handling to allow other plane types (primary and
cursor) to also be placed on the DRM plane list.

v2: Add drm_for_each_legacy_plane() iterator to smooth transition
    of drivers with plane loops.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/drm_fb_helper.c

@@ -291,7 +291,8 @@ bool drm_fb_helper_restore_fbdev_mode(struct drm_fb_helper *fb_helper)
 	drm_warn_on_modeset_not_all_locked(dev);
 
 	list_for_each_entry(plane, &dev->mode_config.plane_list, head)
-		drm_plane_force_disable(plane);
+		if (plane->type != DRM_PLANE_TYPE_PRIMARY)
+			drm_plane_force_disable(plane);
 
 	for (i = 0; i < fb_helper->crtc_count; i++) {
 		struct drm_mode_set *mode_set = &fb_helper->crtc_info[i].mode_set;