gpio-lynxpoint: Allow building as a module

Change CONFIG_GPIO_LYNXPOINT from bool to tristate so that the
gpio-lynxpoint driver can be built as a module.

Add the required glue: an exit function to unregister the driver, and
module information.
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -353,7 +353,7 @@ config GPIO_GE_FPGA
 	  board computers.
 
 config GPIO_LYNXPOINT
-	bool "Intel Lynxpoint GPIO support"
+	tristate "Intel Lynxpoint GPIO support"
 	depends on ACPI && X86
 	select IRQ_DOMAIN
 	help

drivers/gpio/gpio-lynxpoint.c

@@ -469,4 +469,15 @@ static int __init lp_gpio_init(void)
 	return platform_driver_register(&lp_gpio_driver);
 }
 
+static void __exit lp_gpio_exit(void)
+{
+	platform_driver_unregister(&lp_gpio_driver);
+}
+
 subsys_initcall(lp_gpio_init);
+module_exit(lp_gpio_exit);
+
+MODULE_AUTHOR("Mathias Nyman (Intel)");
+MODULE_DESCRIPTION("GPIO interface for Intel Lynxpoint");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:lp_gpio");