UPSTREAM: regulator: pwm: Document pwm-dutycycle-unit and pwm-dutycycle-range

UPSTREAM: regulator: pwm: Document pwm-dutycycle-unit and pwm-dutycycle-range

Document the pwm-dutycycle-unit and pwm-dutycycle-range properties.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Brian Norris <briannorris@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
(cherry picked from commit 58fd822b2e344edae6b4dbc09b19bd0c4a2f8f60)

Change-Id: I029307b54210f2203276a467e947d0fa2e51966d
Signed-off-by: David Wu <david.wu@rock-chips.com>