drm/xe: Enable D3Cold on 'low' VRAM utilization

Now that we eliminated all the mem_access get/put with its
locking issues from the inner calls of migration, we can
allow D3Cold.

Enable it when VRAM utilization is lower then 300Mb. On
higher utilization we only allow D3hot so we don't increase
so much the latency on runtime resume due to the memory
restoration.
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240522170105.327472-7-rodrigo.vivi@intel.comSigned-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_pm.h

@@ -8,12 +8,7 @@
 
 #include <linux/pm_runtime.h>
 
-/*
- * TODO: Threshold = 0 will block D3Cold.
- *       Before we can move this to a higher value (like 300), we need to:
- *           1. rewrite the VRAM save / restore to avoid buffer object locks
- */
-#define DEFAULT_VRAM_THRESHOLD 0 /* in MB */
+#define DEFAULT_VRAM_THRESHOLD 300 /* in MB */
 
 struct xe_device;