drm/dp: add extended receiver capability field present bit

This bit was added to DP Training Aux RD interval with DP 1.3. Via
descriptiion of the spec this field indicates the panels true
capabilities are described in DPCD address space 02200h through 022FFh.

v2: version comment update
v3: version comment correction, commit message update
v4: white space correction
Signed-off-by: NMatt Atwood <matthew.s.atwood@intel.com>
Reviewed-by: NManasi Navare <manasi.d.navare@intel.com>
[manasi: fixup whitespace per Rodrigo's comment]
Signed-off-by: NManasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180723212735.23893-1-matthew.s.atwood@intel.com

include/drm/drm_dp_helper.h

@@ -123,8 +123,9 @@
 # define DP_FRAMING_CHANGE_CAP		    (1 << 1)
 # define DP_DPCD_DISPLAY_CONTROL_CAPABLE     (1 << 3) /* edp v1.2 or higher */
 
-#define DP_TRAINING_AUX_RD_INTERVAL         0x00e   /* XXX 1.2? */
-# define DP_TRAINING_AUX_RD_MASK            0x7F    /* XXX 1.2? */
+#define DP_TRAINING_AUX_RD_INTERVAL             0x00e   /* XXX 1.2? */
+# define DP_TRAINING_AUX_RD_MASK                0x7F    /* DP 1.3 */
+# define DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT	(1 << 7) /* DP 1.3 */
 
 #define DP_ADAPTER_CAP			    0x00f   /* 1.2 */
 # define DP_FORCE_LOAD_SENSE_CAP	    (1 << 0)