regmap: sdw: Remove 8-bit value size restriction

Some SoundWire devices have larger width device specific register
maps, in addition to the standard SoundWire 8-bit map. Update the
helpers to allow accessing arbitrarily sized register values and remove
the explicit 8-bit restriction from regmap_sdw_config_check.

Signed-off-by: Lucas Tanure <tanureal@opensource.cirrus.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20230112171840.2098463-3-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>