ASoC: codec: cs42l56: Drop cs42l56.h

ASoC: codec: cs42l56: Drop cs42l56.h

There is no in-tree user of "include/sound/cs42l56.h", so move
'struct cs42l56_platform_data' to cs42l56.c and remove the header file.
And platform data is mostly for platforms that create
devices non using device tree. CS42L56 is a discontinued product,
there is less possibility that new users will use legacy method
to create devices. So drop cs42l56.h to prepare using GPIOD API.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://patch.msgid.link/20250506-csl42x-v3-2-e9496db544c4@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>