Extend the testing of cache-drop.

- Added cache_drop_all_and_sync_marked_dirty(). If all registers are
  dropped from the cache a regcache_mark_dirty() followed by
  regcache_sync() should not write anything because the cache is empty.

- Added cache_drop_all_and_sync_no_defaults(). This is similar to
  cache_drop_all_and_sync_marked_dirty() except that regcache_mark_dirty()
  is NOT called. All registers were dropped so regcache_sync() should not
  write anything.

- Added cache_drop_all_and_sync_has_defaults(). This is the same as
  cache_drop_all_and_sync_no_defaults() except that the regmap has a
  table of default values.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://msgid.link/r/20240408144600.230848-7-rf@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>