drm/modes: Allow to specify rotation and reflection on the commandline

Rotations and reflections setup are needed in some scenarios to initialise
properly the initial framebuffer. Some drivers already had a bunch of
quirks to deal with this, such as either a private kernel command line
parameter (omapdss) or on the device tree (various panels).

In order to accomodate this, let's create a video mode parameter to deal
with the rotation and reflexion.

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/777da16e42db757c1f5b414b5ca34507097fed5c.1560783090.git-series.maxime.ripard@bootlin.com

include/drm/drm_connector.h

@@ -1025,6 +1025,16 @@ struct drm_cmdline_mode {
 	 * state to one of the DRM_FORCE_* values.
 	 */
 	enum drm_connector_force force;
+
+	/**
+	 * @rotation_reflection:
+	 *
+	 * Initial rotation and reflection of the mode setup from the
+	 * command line. See DRM_MODE_ROTATE_* and
+	 * DRM_MODE_REFLECT_*. The only rotations supported are
+	 * DRM_MODE_ROTATE_0 and DRM_MODE_ROTATE_180.
+	 */
+	unsigned int rotation_reflection;
 };
 
 /**