regulator: sy7636a: Store the epd-pwr-good GPIO locally

Instead of storing the GPIO state in the mfd (where it isn't used) store
it in the regulator.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
Link: https://lore.kernel.org/r/20210803084456.198-7-alistair@alistair23.me


Signed-off-by: Mark Brown <broonie@kernel.org>