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>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 0f04444..58d98dd 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -353,7 +353,7 @@
 	  board computers.
 
 config GPIO_LYNXPOINT
-	bool "Intel Lynxpoint GPIO support"
+	tristate "Intel Lynxpoint GPIO support"
 	depends on ACPI && X86
 	select IRQ_DOMAIN
 	help