drm/i915: Compile out error state without DEBUG_FS

Alexander reported that the compilation of intel_overlay.c was failing
due to an inclusion that was only valid with CONFIG_DEBUG_FS. As the
whole error reporting is only useful with debugfs enabled, remove all
the redundant error state collection code when compiling without
CONFIG_DEBUG_FS.

Reported-by: Alexander Lam <lambchop468@gmail.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1016073..634e1c46 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -874,7 +874,6 @@
 
 /* i915_irq.c */
 void i915_hangcheck_elapsed(unsigned long data);
-void i915_destroy_error_state(struct drm_device *dev);
 extern int i915_irq_emit(struct drm_device *dev, void *data,
 			 struct drm_file *file_priv);
 extern int i915_irq_wait(struct drm_device *dev, void *data,
@@ -911,6 +910,12 @@
 
 void intel_enable_asle (struct drm_device *dev);
 
+#ifdef CONFIG_DEBUG_FS
+extern void i915_destroy_error_state(struct drm_device *dev);
+#else
+#define i915_destroy_error_state(x)
+#endif
+
 
 /* i915_mem.c */
 extern int i915_mem_alloc(struct drm_device *dev, void *data,
@@ -1091,8 +1096,10 @@
 extern int intel_trans_dp_port_sel (struct drm_crtc *crtc);
 
 /* overlay */
+#ifdef CONFIG_DEBUG_FS
 extern struct intel_overlay_error_state *intel_overlay_capture_error_state(struct drm_device *dev);
 extern void intel_overlay_print_error_state(struct seq_file *m, struct intel_overlay_error_state *error);
+#endif
 
 /**
  * Lock test for when it's just for synchronization of ring access.