rtc: rk808: Name RK805 in Kconfig for RTC_DRV_RK808

The RK808 and RK805 PMICs are using a similar register map.
We can reuse the rtc driver for the RK805 PMIC. So let's add
the RK805 in the Kconfig description.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Joseph Chen <chenjh@rock-chips.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>