mfd: twl6040: Use maple tree register cache

The twl6040 is only capable of performing single register read and write
operations which means it gains no advantage from using a rbtree register
cache, convert it to using the more modern maple tree register cache
instead. This should be more efficient.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230609-mfd-twl6040-maple-v1-1-3493d051cd6f@kernel.org


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