gpio: arizona: Add support for GPIOs that need to be maintained

The Arizona devices only maintain the state of output GPIOs whilst the
CODEC is active, this can cause issues if the CODEC suspends whilst
something is relying on the state of one of its GPIOs. However, in
many systems the CODEC GPIOs are used for audio related features
and thus the state of the GPIOs is unimportant whilst the CODEC is
suspended. Often keeping the CODEC resumed in such a system would
incur a power impact that is unacceptable.

Allow the user to select whether a GPIO output should keep the
CODEC resumed, by adding a flag through the second cell of the GPIO
specifier in device tree.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>