drm: Make mode->flags u32

The mode flags are direclty exposed in the uapi as u32. Use the
same size type to store them internally.
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200428171940.19552-8-ville.syrjala@linux.intel.com

include/drm/drm_modes.h

@@ -323,7 +323,7 @@ struct drm_display_mode {
 	 *  - DRM_MODE_FLAG_3D_SIDE_BY_SIDE_HALF: frame split into left and
 	 *    right parts.
 	 */
-	unsigned int flags;
+	u32 flags;
 
 	/**
 	 * @width_mm: