regulator: pfuze100: add optional disable switch-regulators binding

This binding is used to keep the backward compatibility with the current
dtb's [1]. The binding informs the driver that the unused switch regulators
can be disabled.
If it is not specified, the driver doesn't disable the switch regulators.

[1] https://patchwork.kernel.org/patch/10490381/



Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>