mfd: rk808: Split into core and i2c

Split rk808 into a core and an i2c part in preparation for
SPI support.

Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com> # for RTC
Tested-by: Diederik de Haas <didi.debian@cknow.org> # Rock64, Quartz64 Model A + B
Tested-by: Vincent Legoll <vincent.legoll@gmail.com> # Pine64 QuartzPro64
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20230504173618.142075-6-sebastian.reichel@collabora.com


Signed-off-by: Lee Jones <lee@kernel.org>