drm/i915: use GMBUS to manage i2c links

Use the GMBUS interface rather than direct bit banging to grab the EDID
over DDC (and for other forms of auxiliary communication with external
display controllers). The hope is that this method will be much faster
and more reliable than bit banging for fetching EDIDs from buggy monitors
or through switches, though we still preserve the bit banging as a
fallback in case GMBUS fails.

Based on an original patch by Jesse Barnes.

Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 208a4ec..9a87ec5 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1490,7 +1490,7 @@
 	/* We should parse the EDID data and find out if it has an audio sink
 	 */
 
-	ret = intel_ddc_get_modes(connector, intel_dp->base.ddc_bus);
+	ret = intel_ddc_get_modes(connector, &intel_dp->adapter);
 	if (ret) {
 		if ((IS_eDP(intel_dp) || IS_PCH_eDP(intel_dp)) &&
 		    !dev_priv->panel_fixed_mode) {
@@ -1705,7 +1705,6 @@
 
 	intel_dp_i2c_init(intel_dp, intel_connector, name);
 
-	intel_encoder->ddc_bus = &intel_dp->adapter;
 	intel_encoder->hot_plug = intel_dp_hot_plug;
 
 	if (output_reg == DP_A || IS_PCH_eDP(intel_dp)) {