drm/i915: PM irq enabling is generic on gen8, too

No need to list all the platforms explicitly.

The prefix is a bit inconsistent since we usually pick gen8_ for GT
related functions. But this anti-pattern is already established with snb,
so material for a different patch.

Cc: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -1407,7 +1407,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	spin_lock_irq(&dev_priv->irq_lock);
 	pm_iir = dev_priv->rps.pm_iir;
 	dev_priv->rps.pm_iir = 0;
-	if (IS_BROADWELL(dev_priv->dev) || IS_CHERRYVIEW(dev_priv->dev))
+	if (INTEL_INFO(dev_priv->dev)->gen >= 8)
 		bdw_enable_pm_irq(dev_priv, dev_priv->pm_rps_events);
 	else {
 		/* Make sure not to corrupt PMIMR state used by ringbuffer */