dt-bindings: pinctrl: add a 'pinctrl-use-default' property

Pin setup may be optional in some cases such as the reset default works
or the pin setup is done by the bootloader. In these cases, it is optional
for the OS to support managing the pin controller and pin setup. In order
to support this scenario, add a property 'pinctrl-use-default' to indicate
that the pin configuration is optional.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>