ASoC: cs4271: flat regcache, trivial simplifications

- Switch to REGCACHE_FLAT, the whole overhead of RBTREE is not worth it
  with non sparse register set in the address range 1..7.
- Move register width to central location

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Link: https://lore.kernel.org/r/20230410223902.2321834-3-alexander.sverdlin@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>