regulator: act8865 regulator modes and suspend states

Add documentation for act8865 regulator modes and suspend states.
Add active-semi,8865-regulator.h file for device tree binding constants
for act8865 regulators.

Signed-off-by: Raag Jadav <raagjadav@gmail.com>
Link: https://lore.kernel.org/r/1565721176-8955-3-git-send-email-raagjadav@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>