drm/i915: Kill intel_runtime_pm_disable()

intel_runtime_pm_disable() takes an extra rpm reference which combined
with the one we leak from intel_display_set_init_power() leaves the
usage count at <original>+1 after the driver has been unloaded.
The original ref is dropped explicitly in intel_runtime_pm_enable().
So the next time we load the driver we can no longer do runtime PM ever.

This used to work, but
commit 292b990e86ab ("drm/i915: Update power domains on readout.")
broke things by not dropping the init power domain during fbdev
teardown. Based on the comment in intel_power_domains_fini(), the
way it used to to work wasn't intentional. As in we weren't supposed
to drop the init power during driver unload. And since we no longer
do, we now leak an extra rpm reference.

So fix things by throwing intel_runtime_pm_disable() to the bin, so
that the only leaked reference comes from the init power domain.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Fixes: 292b990e86ab ("drm/i915: Update power domains on readout.")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446815313-9490-2-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -1846,21 +1846,6 @@ int intel_power_domains_init(struct drm_i915_private *dev_priv)
 	return 0;
 }
 
-static void intel_runtime_pm_disable(struct drm_i915_private *dev_priv)
-{
-	struct drm_device *dev = dev_priv->dev;
-	struct device *device = &dev->pdev->dev;
-
-	if (!HAS_RUNTIME_PM(dev))
-		return;
-
-	if (!intel_enable_rc6(dev))
-		return;
-
-	/* Make sure we're not suspended first. */
-	pm_runtime_get_sync(device);
-}
-
 /**
  * intel_power_domains_fini - finalizes the power domain structures
  * @dev_priv: i915 device instance
@@ -1871,8 +1856,6 @@ static void intel_runtime_pm_disable(struct drm_i915_private *dev_priv)
  */
 void intel_power_domains_fini(struct drm_i915_private *dev_priv)
 {
-	intel_runtime_pm_disable(dev_priv);
-
 	/* The i915.ko module is still not prepared to be loaded when
 	 * the power well is not enabled, so just enable it in case
 	 * we're going to unload/reload. */