drm/i915: Enable GuC firmware log

Allocate a GEM object to hold GuC log data. A debugfs interface
(i915_guc_log_dump) is provided to print out the log content.

v2:
    Add struct members at point of use [Chris Wilson]

v6:
    Rebased

Issue: VIZ-4884
Signed-off-by: Alex Dai <yu.dai@intel.com>
Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tom O'Rourke <Tom.O'Rourke@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_guc.h b/drivers/gpu/drm/i915/intel_guc.h
index be3cad8..5b51b05 100644
--- a/drivers/gpu/drm/i915/intel_guc.h
+++ b/drivers/gpu/drm/i915/intel_guc.h
@@ -56,6 +56,7 @@
 	struct intel_guc_fw guc_fw;
 
 	uint32_t log_flags;
+	struct drm_i915_gem_object *log_obj;
 
 	struct drm_i915_gem_object *ctx_pool_obj;
 	struct ida ctx_ids;