bus: vexpress-config: Support building as module

Enable building vexpress-config driver as a module.

Cc: Lorenzo Pieralisi <[e-mail]>
Cc: Linus Walleij <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Reviewed-by: Sudeep Holla <[e-mail]>
Acked-by: Liviu Dudau <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

drivers/bus/Kconfig

···
 	  needed to use on-board devices connected to UniPhier SoCs.
 
 config VEXPRESS_CONFIG
-	bool "Versatile Express configuration bus"
+	tristate "Versatile Express configuration bus"
 	default y if ARCH_VEXPRESS
 	depends on ARM || ARM64
 	depends on OF

drivers/bus/vexpress-config.c

···
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/io.h>
+#include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/of_device.h>
···
 	{ "vexpress-syscfg", },
 	{},
 };
+MODULE_DEVICE_TABLE(platform, vexpress_syscfg_id_table);
 
 static struct platform_driver vexpress_syscfg_driver = {
 	.driver.name = "vexpress-syscfg",
 	.id_table = vexpress_syscfg_id_table,
 	.probe = vexpress_syscfg_probe,
 };
-
-static int __init vexpress_syscfg_init(void)
-{
-	return platform_driver_register(&vexpress_syscfg_driver);
-}
-core_initcall(vexpress_syscfg_init);
+module_platform_driver(vexpress_syscfg_driver);
+MODULE_LICENSE("GPL v2");