regulator: RK808: Add regulator driver for RK808

The regulator module consists of 4 DCDCs, 8 LDOs and 2 switches.
The output voltages are configurable and are meant to supply power
to the main processor and other components

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Mark Brown <broonie@linaro.org>