drm/i915: add aux_ch_ctl_reg to struct intel_dp

This way we can remove some duplicated code and avoid more mistakes
and regressions with these registers in the future.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index febed9a..f21e226 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -366,6 +366,7 @@
 
 struct intel_dp {
 	uint32_t output_reg;
+	uint32_t aux_ch_ctl_reg;
 	uint32_t DP;
 	uint8_t  link_configuration[DP_LINK_CONFIGURATION_SIZE];
 	bool has_audio;