devicetree: bindings: bd718x7: document HW state related ROHM specific properties

devicetree: bindings: bd718x7: document HW state related ROHM specific properties

Add ROHM BD71837 / BD71847 specific device tree bindings for
controlling the PMIC shutdown/reset states and voltages for
different HW states. The PMIC was designed to be used with NXP
i.MX8 SoC and it supports SNVS low power state which seems to
be typical for NXP i.MX SoCs. However, when SNVS is used we must
not allow SW to control enabling/disabling those regulators which
are crucial for system to boot as there is a HW limitation which
causes SW controlled regulators to be kept shut down after SNVS
reset.

Allow setting the SNVS to be used as reset target state and allow
marking those regulators which are critical for boot.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Tested-by: Angus Ainslie <angus@akkea.ca>
Reviewed-by: Angus Ainslie <angus@akkea.ca>
Signed-off-by: Mark Brown <broonie@kernel.org>
(cherry picked from commit f43d1b388f9be4aa47ed42c33659243a675c5c76)