regulator: max77802: Document binding for regulator operating modes

regulator: max77802: Document binding for regulator operating modes

Some regulators from the max77802 PMIC support to be configured in one
of two operating mode: Output ON (normal) and Output On Low Power Mode.
Not all regulators support these two modes and for some of them, the
mode can be changed while the system is running in normal operation
while others only support their mode to be changed on system suspend.

Extend the max77802 PMIC binding by documenting the possible operating
modes values so the regulators modes can be configured correctly.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Mark Brown <broonie@kernel.org>