drm/stm: ltdc: add support of horizontal & vertical mirroring

Support of vertical & horizontal mirroring features thanks to
the plane rotation property.
Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220603134547.593790-1-yannick.fertre@foss.st.com

drivers/gpu/drm/stm/ltdc.h

@@ -29,6 +29,7 @@ struct ltdc_caps {
 	bool plane_reg_shadow;	/* plane shadow registers ability */
 	bool crc;		/* cyclic redundancy check supported */
 	bool dynamic_zorder;	/* dynamic z-order */
+	bool plane_rotation;	/* plane rotation */
 };
 
 #define LTDC_MAX_LAYER	4