pinctrl: abx500: force-convert to generic mux bindings

This converts the ABx500 pin controller and all associated device
trees to use the standard, generic mux bindings for pin controllers.
There are no such device trees deployed in the wild so this is
safe to do to set a good example.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>