extcon: gpio: Move platform data into state container

This moves the platform data settings from the platform data
struct and into the state container, saving some unnecessary
references and simplifying things a bit.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
[cw00.choi: Add FIXME comment of extcon_id]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>