mfd: rk8xx: Convert to use maple tree register cache

The maple tree register cache is based on a much more modern data structure
than the rbtree cache and makes optimisation choices which are probably
more appropriate for modern systems than those made by the rbtree cache.

Signed-off-by: Bo Liu <liubo03@inspur.com>
Link: https://lore.kernel.org/r/20240206071314.8721-13-liubo03@inspur.com
Signed-off-by: Lee Jones <lee@kernel.org>

mfd: rk8xx: Add rk806 support

Add support for SPI connected rk806, which is used by the RK3588
evaluation boards. The PMIC is advertised to support I2C and SPI,
but the evaluation boards all use SPI. Thus only SPI support is
added here.

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/20230504173618.142075-9-sebastian.reichel@collabora.com
Signed-off-by: Lee Jones <lee@kernel.org>