gpio: Initial support for ROHM bd70528 GPIO block

ROHM BD70528 PMIC has 4 GPIO pins. Allow them to be
controlled by GPIO framework.

IRQs are handled by regmap-irq and GPIO driver is not
aware of the irq usage.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>