gpio: ep93xx: refactor base IRQ number

- use predefined constants instead of plain numbers
- use provided bank IRQ number instead of defined constant
  for port F

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>