CHROMIUM: rk808: rockchip: add pmic rk808 driver.

Rk808 is a pmic used in rk3288 soc, it contains rtc, regulator

BUG=chrome-os-partner:30167
TEST=Build and boot on veyron. Set the regulator voltage, read the register.

Change-Id: I16988f96cc979cdf327df55a32645d97ffb7101a
Signed-off-by: Chris Zhong <zyw@rock-chips.com>