gpio: Add gpio delay driver

This driver implements a GPIO enable/disable delay. It supports a list
of GPIO outputs, which ramp-up/ramp-down delay can be specified at
consumer location.
The main purpose is to address external, passive delays upon line
voltage changes.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>