rtc: rk808: Add RK809 and RK817 support.

RK809 and RK817 are power management IC chips for multimedia products.
Most of their functions and registers are same, including the rtc.

Signed-off-by: Tony Xie <tony.xie@rock-chips.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>