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_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index e797157..080ea3b 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -421,6 +421,7 @@
 	}
 }
 
+#ifdef CONFIG_DEBUG_FS
 static struct drm_i915_error_object *
 i915_error_object_create(struct drm_device *dev,
 			 struct drm_gem_object *src)
@@ -744,6 +745,9 @@
 	if (error)
 		i915_error_state_free(dev, error);
 }
+#else
+#define i915_capture_error_state(x)
+#endif
 
 static void i915_report_and_clear_eir(struct drm_device *dev)
 {