pinctrl: ocelot: Always register GPIO driver

pinctrl: ocelot: Always register GPIO driver

This fixes the situation where the GPIO controller is not
used as an interrupt controller as well.

Previously, the driver would silently fail to register even the
GPIO's. With this change, the driver will only register as an
interrupt controller if a parent interrupt is provided.

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Link: https://lore.kernel.org/r/20200513125532.24585-2-lars.povlsen@microchip.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>