ixp4xx_eth: Stop referring to GPIOs

The driver is being passed interrupts, then looking up the
same interrupts as GPIOs a second time to convert them into
interrupts and set properties on them.

This is pointless: the GPIO and irqchip APIs of a GPIO chip
are orthogonal. Just request the interrupts and be done
with it, drop reliance on any GPIO functions or definitions.

Use devres-managed functions and add a small devress quirk
to unregister the clock as well and we can rely on devres
to handle all the resources and cut down a bunch of
boilerplate in the process.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>