drm/i915: get a runtime PM ref for the deferred GT powersave enabling

At least on VLV but probably on other platforms too we depend on RC6
being enabled for RPM, so disable RPM until the delayed RC6 enabling
completes.

v2:
- explain the reason for the _noresume version of RPM get (Daniel)
- use the simpler 'if (schedule_work()) rpm_get();' instead of
  'if (!cancel_work_sync()) rpm_get(); schedule_work();'

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.c

@@ -782,7 +782,7 @@ int i915_reset(struct drm_device *dev)
 		 * previous concerns that it doesn't respond well to some forms
 		 * of re-init after reset. */
 		if (INTEL_INFO(dev)->gen > 5)
-			intel_enable_gt_powersave(dev);
+			intel_reset_gt_powersave(dev);
 
 		intel_hpd_init(dev);
 	} else {
@@ -951,6 +951,9 @@ static int intel_runtime_suspend(struct device *device)
 	struct drm_device *dev = pci_get_drvdata(pdev);
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	if (WARN_ON_ONCE(!dev_priv->rps.enabled))
+		return -ENODEV;
+
 	WARN_ON(!HAS_RUNTIME_PM(dev));
 	assert_force_wake_inactive(dev_priv);