drm/i915: Eliminate PORT_HOTPLUG_EN setup from gen3/4 irq_postinstall

We've already cleared PORT_HOTPLUG_EN in the .irq_preinstall hook
so doing it again in the .irq_postinstall is pointless.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170818183705.27850-8-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/i915_irq.c

@@ -3761,9 +3761,6 @@ static int i915_irq_postinstall(struct drm_device *dev)
 		I915_USER_INTERRUPT;
 
 	if (I915_HAS_HOTPLUG(dev_priv)) {
-		i915_hotplug_interrupt_update(dev_priv, 0xffffffff, 0);
-		POSTING_READ(PORT_HOTPLUG_EN);
-
 		/* Enable in IER... */
 		enable_mask |= I915_DISPLAY_PORT_INTERRUPT;
 		/* and unmask in IMR */
@@ -3960,9 +3957,6 @@ static int i965_irq_postinstall(struct drm_device *dev)
 
 	GEN3_IRQ_INIT(, dev_priv->irq_mask, enable_mask);
 
-	i915_hotplug_interrupt_update(dev_priv, 0xffffffff, 0);
-	POSTING_READ(PORT_HOTPLUG_EN);
-
 	i915_enable_asle_pipestat(dev_priv);
 
 	return 0;