extcon: gpio: Add support for active-low presence to detect pins

This patch add 'gpio_active_low' field to 'struct gpio_extcon_data'
to check whether gpio active state is 1(high) or 0(low).

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>