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: NJean Delvare <jdelvare@suse.de>
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Acked-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>