i2c: mux: arb-gpio: Rewrite to use GPIO descriptors

Instead of complex code picking GPIOs out of the device tree
and keeping track of polarity for each GPIO line, use descriptors
and pull polarity handling into the gpiolib.

We look for "our-claim" and "their-claim" since the gpiolib
code will try e.g. "our-claim-gpios" and "our-claim-gpio" in
turn to locate these GPIO lines from the device tree.

Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Doug Anderson <dianders@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Peter Rosin <peda@axentia.se>