power: reset: xgene-reboot: use builtin_platform_driver() to simplify code

The xgene_reboot_init() doesn't do anything special, so it can use the
builtin_platform_driver() macro to eliminate boilerplate code.
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20230807131951.3443880-4-yangyingliang@huawei.comSigned-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/reset/xgene-reboot.c

@@ -87,9 +87,4 @@ static struct platform_driver xgene_reboot_driver = {
 		.of_match_table = xgene_reboot_of_match,
 	},
 };
-
-static int __init xgene_reboot_init(void)
-{
-	return platform_driver_register(&xgene_reboot_driver);
-}
-device_initcall(xgene_reboot_init);
+builtin_platform_driver(xgene_reboot_driver);