ARM: ixp4xx: convert remaining users to use gpiolib

A few call sites inside mach-ixp4xx were still using the custom
ixp4xx GPIO API with gpio_line_* accessors, convert all these
to use the standard gpiolib functions instead. Also attempt to
request and label all GPIOs before use. Move the GPIO requests
to per-machine device_initcalls() so we are not dependent on the
GPIO chip to be available at machine_init time.

Cc: Imre Kaloz <kaloz@openwrt.org>
Cc: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>