power: pmic: rk816: support rk816 pmic

The RK816 is a Power Management IC (PMIC) for multimedia
and handheld devices. They contains the following components:
    - Regulators(4*BUCKs, 1*BOOST, 6*LDOs, 1*SWITCH)
    - RTC
    - Clocking

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>