drm/i915/dp: Explicitly request 8/10 channel coding

It's not clear what a sink would do if you wrote zero to this register -
which I guess would mean "I don't support any channel encodings, good
luck" - but let's not find out.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -769,6 +769,7 @@ intel_dp_mode_set(struct drm_encoder *encoder, struct drm_display_mode *mode,
 	memset(intel_dp->link_configuration, 0, DP_LINK_CONFIGURATION_SIZE);
 	intel_dp->link_configuration[0] = intel_dp->link_bw;
 	intel_dp->link_configuration[1] = intel_dp->lane_count;
+	intel_dp->link_configuration[8] = DP_SET_ANSI_8B10B;
 
 	/*
 	 * Check for DPCD version > 1.1 and enhanced framing support