drm/dp: Add definition for Display Control DPCD Registers capability size

This is used when reading Display Control capability Registers on the sink
device.

cc: dri-devel@lists.freedesktop.org
Signed-off-by: Yetunde Adebisi <yetundex.adebisi@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459865452-9138-2-git-send-email-yetundex.adebisi@intel.com

include/drm/drm_dp_helper.h

@@ -621,6 +621,7 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI
 #define DP_BRANCH_OUI_HEADER_SIZE	0xc
 #define DP_RECEIVER_CAP_SIZE		0xf
 #define EDP_PSR_RECEIVER_CAP_SIZE	2
+#define EDP_DISPLAY_CTL_CAP_SIZE	3
 
 void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]);
 void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]);