drm/i915: Hack to tie both common lanes together on chv

It looks like frobbing the cmnreset line on pne PHY disturbs the other
PHY on chv. The result is a black screen. On HDMI it's just a flash of
black, but DP usually falls over and can't get back up.

As a workaround set up the power domains so that both common lane
wells power up and down together. I also tried leaving the cmnreset
deasserted even the if the power well goes down but that didn't seem
acceptable to the PHY.
Reviewed-by: NRafael Barbalho <rafael.barbalho@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -6877,13 +6877,23 @@ static struct i915_power_well chv_power_wells[] = {
 #endif
 	{
 		.name = "dpio-common-bc",
-		.domains = CHV_DPIO_CMN_BC_POWER_DOMAINS,
+		/*
+		 * XXX: cmnreset for one PHY seems to disturb the other.
+		 * As a workaround keep both powered on at the same
+		 * time for now.
+		 */
+		.domains = CHV_DPIO_CMN_BC_POWER_DOMAINS | CHV_DPIO_CMN_D_POWER_DOMAINS,
 		.data = PUNIT_POWER_WELL_DPIO_CMN_BC,
 		.ops = &chv_dpio_cmn_power_well_ops,
 	},
 	{
 		.name = "dpio-common-d",
-		.domains = CHV_DPIO_CMN_D_POWER_DOMAINS,
+		/*
+		 * XXX: cmnreset for one PHY seems to disturb the other.
+		 * As a workaround keep both powered on at the same
+		 * time for now.
+		 */
+		.domains = CHV_DPIO_CMN_BC_POWER_DOMAINS | CHV_DPIO_CMN_D_POWER_DOMAINS,
 		.data = PUNIT_POWER_WELL_DPIO_CMN_D,
 		.ops = &chv_dpio_cmn_power_well_ops,
 	},