drm/i915/guc: Call invalidate after changing the vfunc

To make this operation a bit cleaner, we should make sure that the HW
can catch up by calling the new implementation right away.
Note that currently we're only touching the vfunc at module load time
(before GuC is even loaded), so this shouldn't cause any functional
changes.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171213221352.7173-4-michal.winiarski@intel.com

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -3552,6 +3552,8 @@ void i915_ggtt_enable_guc(struct drm_i915_private *i915)
 	GEM_BUG_ON(i915->ggtt.invalidate != gen6_ggtt_invalidate);
 
 	i915->ggtt.invalidate = guc_ggtt_invalidate;
+
+	i915_ggtt_invalidate(i915);
 }
 
 void i915_ggtt_disable_guc(struct drm_i915_private *i915)
@@ -3560,6 +3562,8 @@ void i915_ggtt_disable_guc(struct drm_i915_private *i915)
 	GEM_BUG_ON(i915->ggtt.invalidate != guc_ggtt_invalidate);
 
 	i915->ggtt.invalidate = gen6_ggtt_invalidate;
+
+	i915_ggtt_invalidate(i915);
 }
 
 void i915_gem_restore_gtt_mappings(struct drm_i915_private *dev_priv)