regulator: add documentation for ACT8945A's regulator DT bindings

This patch adds documentation for the DT bindings of the regulator
subdevice of ACT8945A MFD.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
1 file changed