drm/i915: re-init modeset hw state after gpu reset

After a gpu reset we need to re-init some of the hw state we only
initialize when modeset is enabled, like rc6, hw contexts or render/GT
core clock gating and workaround register settings.

Note that this patch has a small change in the resume code:
- rc6 on gen6+ is only restored for the modeset case (for more
  consistency with other callsites). This is no problem because recent
  kernels refuse to load drm/i915 without kms on gen6+
- rc6/emon on ilk is only restored for the modeset case. This is no
  problem because rc6 is disabled by default on ilk, and ums on ilk
  has never really been a supported option outside of horrible rhel
  backports.

v2: Chris Wilson noticed that we not only fail to restore the clock
gating settings after gpu reset.

v3: Move the call to modeset_init_hw in _reset out of the
struct_mutext protected area - other callers don't hold it, too.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_suspend.c

@@ -879,17 +879,7 @@ int i915_restore_state(struct drm_device *dev)
 	mutex_unlock(&dev->struct_mutex);
 
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
-		intel_init_clock_gating(dev);
-
-	if (IS_IRONLAKE_M(dev)) {
-		ironlake_enable_drps(dev);
-		intel_init_emon(dev);
-	}
-
-	if (INTEL_INFO(dev)->gen >= 6) {
-		gen6_enable_rps(dev_priv);
-		gen6_update_ring_freq(dev_priv);
-	}
+		intel_modeset_init_hw(dev);
 
 	mutex_lock(&dev->struct_mutex);