drm/i915: Fix system hang with EI UP masked on Haswell

Previously with commit a9c1f90
("drm/i915: Don't mask EI UP interrupt on IVB|SNB") certain,
seemingly unrelated bit (GEN6_PM_RP_UP_EI_EXPIRED) was needed
to be unmasked for IVB and SNB in order to prevent system hang
with chained batchbuffers.

Our CI was seeing incomplete results with tests that used
chained batches and it was found out that HSW needs to have this
same bit unmasked to reliably survive chained batches.

Always unmask GEN6_PM_RP_UP_EI_EXPIRED on Haswell to
prevent system hang with batch chaining.

Testcase: igt/gem_exec_fence/nb-await-default
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100672
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1492082127-29007-1-git-send-email-mika.kuoppala@intel.com

drivers/gpu/drm/i915/i915_irq.c

@@ -4252,12 +4252,12 @@ void intel_irq_init(struct drm_i915_private *dev_priv)
 	dev_priv->rps.pm_intrmsk_mbz = 0;
 
 	/*
-	 * SNB,IVB can while VLV,CHV may hard hang on looping batchbuffer
+	 * SNB,IVB,HSW can while VLV,CHV may hard hang on looping batchbuffer
 	 * if GEN6_PM_UP_EI_EXPIRED is masked.
 	 *
 	 * TODO: verify if this can be reproduced on VLV,CHV.
 	 */
-	if (INTEL_INFO(dev_priv)->gen <= 7 && !IS_HASWELL(dev_priv))
+	if (INTEL_INFO(dev_priv)->gen <= 7)
 		dev_priv->rps.pm_intrmsk_mbz |= GEN6_PM_RP_UP_EI_EXPIRED;
 
 	if (INTEL_INFO(dev_priv)->gen >= 8)