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: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20231001-mfd-rk88x-maple-v1-1-90434cfb2f90@kernel.org


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