mfd: rk808: Add RK805 support

The RK805 chip is a Power Management IC (PMIC) for multimedia and handheld
devices. It contains the following components:

    - Regulators
    - RTC
    - Clocking

Both RK808 and RK805 chips are using a similar register map,
so we can reuse the RTC and Clocking functionality.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Joseph Chen <chenjh@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>