drm/i915: Enable PM Interrupts target via Display Interface.

In BDW, Apart from unmasking up/down threshold interrupts. we need
to umask bit 32 of PM_INTRMASK to route interrupts to target via Display
Interface.

v2: Add (1<<31) mask (Ville)

v3: Add Gen check for the mask (ville)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -5311,6 +5311,7 @@ enum punit_power_well {
 #define VLV_RCEDATA				0xA0BC
 #define GEN6_RC6pp_THRESHOLD			0xA0C0
 #define GEN6_PMINTRMSK				0xA168
+#define GEN8_PMINTR_REDIRECT_TO_NON_DISP	(1<<31)
 #define VLV_PWRDWNUPCTL				0xA294
 
 #define GEN6_PMISR				0x44020

drivers/gpu/drm/i915/intel_pm.c

@@ -3114,6 +3114,9 @@ static u32 gen6_rps_pm_mask(struct drm_i915_private *dev_priv, u8 val)
 	if (INTEL_INFO(dev_priv->dev)->gen <= 7 && !IS_HASWELL(dev_priv->dev))
 		mask |= GEN6_PM_RP_UP_EI_EXPIRED;
 
+	if (IS_GEN8(dev_priv->dev))
+		mask |= GEN8_PMINTR_REDIRECT_TO_NON_DISP;
+
 	return ~mask;
 }