drm/dp: Add defines for latency in sink

Add defines for dpcd register 2009 (synchronization latency
in sink).

v2:
 - add spec version (Daniel)
 - use register name as is in spec,only drop excess
   from end (jani)
 - add the full register contents (jani)
[Rodrigo fixed spec version when merging]

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
CC: Puthikorn Voravootivat <puthik@chromium.org>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Vathsala Nagaraju <vathsala.nagaraju@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1506419953-32605-1-git-send-email-vathsala.nagaraju@intel.comSigned-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

include/drm/drm_dp_helper.h

@@ -735,6 +735,12 @@
 # define DP_PSR_SINK_INTERNAL_ERROR         7
 # define DP_PSR_SINK_STATE_MASK             0x07
 
+#define DP_SYNCHRONIZATION_LATENCY_IN_SINK		0x2009 /* edp 1.4 */
+# define DP_MAX_RESYNC_FRAME_COUNT_MASK			(0xf << 0)
+# define DP_MAX_RESYNC_FRAME_COUNT_SHIFT		0
+# define DP_LAST_ACTUAL_SYNCHRONIZATION_LATENCY_MASK	(0xf << 4)
+# define DP_LAST_ACTUAL_SYNCHRONIZATION_LATENCY_SHIFT	4
+
 #define DP_RECEIVER_ALPM_STATUS		    0x200b  /* eDP 1.4 */
 # define DP_ALPM_LOCK_TIMEOUT_ERROR	    (1 << 0)