drm: Add PSR version 3 macro

eDP 1.4a specification defines PSR version 3, it PSR2 with the
addition of Y-coordinate support when doing selective update.
Signed-off-by: NJosé Roberto de Souza <jose.souza@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180317013828.24182-1-jose.souza@intel.com

include/drm/drm_dp_helper.h

@@ -288,6 +288,7 @@
 #define DP_PSR_SUPPORT                      0x070   /* XXX 1.2? */
 # define DP_PSR_IS_SUPPORTED                1
 # define DP_PSR2_IS_SUPPORTED		    2	    /* eDP 1.4 */
+# define DP_PSR2_WITH_Y_COORD_IS_SUPPORTED  3	    /* eDP 1.4a */
 
 #define DP_PSR_CAPS                         0x071   /* XXX 1.2? */
 # define DP_PSR_NO_TRAIN_ON_EXIT            1