regulator: fixed: provide bindings using power domain

Define bindings for fixed regulator using power domain performance state
to enable/disable corresponding regulator.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20201023131925.334864-2-dmitry.baryshkov@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>