power: regulator: rk808: add rk818 support

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.

Signed-off-by: Jacob Chen <jacob-chen@iotwrt.com>
Reviewed-by: Simon Glass <sjg@chromium.org>