Input: gpio_keys_polled - allow specifying name of input device

Instead of hardcoding the input name to the driver name
('gpio-keys-polled'), allow specifying the name of the device via
"label" property. If the property is not present (nor name is set in
board-supplied platform data), we'll default to the old name.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>