drm/xe/pm: Add vram_d3cold_threshold for d3cold capable device

Do not register vram_d3cold_threshold device sysfs universally
for each gfx device, only register sysfs and set the threshold
value for d3cold capable devices.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/all/20230802070449.2426563-1-anshuman.gupta@intel.com/Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_pm.c

@@ -154,8 +154,11 @@ void xe_pm_init(struct xe_device *xe)
 	drmm_mutex_init(&xe->drm, &xe->d3cold.lock);
 
 	xe->d3cold.capable = xe_pm_pci_d3cold_capable(pdev);
+
+	if (xe->d3cold.capable) {
 		xe_device_sysfs_init(xe);
 		xe_pm_set_vram_threshold(xe, DEFAULT_VRAM_THRESHOLD);
+	}
 
 	xe_pm_runtime_init(xe);
 }