drm/i915: Clear FORCEWAKE when taking over from BIOS

Some BIOSes may forcibly suspend RC6 during their operation which
trigger a warning as we find the hardware in a perplexing state upon
first use. So far that appears to be the worst symptom as fortuituously
we use the same values as the BIOS for programming the FORCEWAKE register.

Reported-by: Oleksij Rempel <bug-track@fisher-privat.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 3281434..4728d30 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1264,6 +1264,7 @@
 
 extern void intel_irq_init(struct drm_device *dev);
 extern void intel_gt_init(struct drm_device *dev);
+extern void intel_gt_reset(struct drm_device *dev);
 
 void i915_error_state_free(struct kref *error_ref);