drm/i915: Record DERRMR, FORCEWAKE and RING_CTL in error-state

These are useful for investigating hangs involving WAIT_FOR_EVENT.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Apply a droplet of Future-Proof in the if-ladder.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -188,10 +188,13 @@ struct drm_i915_error_state {
 	u32 pgtbl_er;
 	u32 ier;
 	u32 ccid;
+	u32 derrmr;
+	u32 forcewake;
 	bool waiting[I915_NUM_RINGS];
 	u32 pipestat[I915_MAX_PIPES];
 	u32 tail[I915_NUM_RINGS];
 	u32 head[I915_NUM_RINGS];
+	u32 ctl[I915_NUM_RINGS];
 	u32 ipeir[I915_NUM_RINGS];
 	u32 ipehr[I915_NUM_RINGS];
 	u32 instdone[I915_NUM_RINGS];