gpio: dwapb: Use generic request, free and set_config

This way GPIO will be denied on pins already claimed by other devices
and basic pin configuration (pull-up, pull-down etc.) can be done
through the userspace GPIO API.

Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>