drm/i915: Use vblank_disable_immediate on gen2

The vblank timestamp->counter guesstimator seems to be
working sufficiently well, so there's no reason not to
disable vblank interrupts ASAP even on gen2.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190322180804.3300-2-ville.syrjala@linux.intel.comAcked-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_irq.c

@@ -4642,12 +4642,6 @@ void intel_irq_init(struct drm_i915_private *dev_priv)
 	else if (INTEL_GEN(dev_priv) >= 3)
 		dev->driver->get_vblank_counter = i915_get_vblank_counter;
 
-	/*
-	 * Opt out of the vblank disable timer on everything except gen2.
-	 * Gen2 doesn't have a hardware frame counter and so depends on
-	 * vblank interrupts to produce sane vblank seuquence numbers.
-	 */
-	if (!IS_GEN(dev_priv, 2))
 	dev->vblank_disable_immediate = true;
 
 	/* Most platforms treat the display irq block as an always-on