regulator: rk808: Add regulator driver for RK818

Add support for the rk818 regulator. The regulator module consists
of 4 DCDCs, 9 LDOs, 1 switch and 1 BOOST converter which is used to
power OTG and HDMI5V.

The output voltages are configurable and are meant to supply power
to the main processor and other components.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>