ASoC: cs35l56: Add common code for factory calibration

ASoC: cs35l56: Add common code for factory calibration

Add core code to support factory calibration. This can be used by both
the ASoC and HDA drivers.

This code consists of implementations of debugfs handlers for three
debugfs files used to start factory calibration and read the results.

This is not a full implementation of debugfs files. There are some
requirements to synchronize with the rest of the amp driver, and the way
this is done is significantly different between ASoC and HDA. Therefore
cs35l56-shared.c provides the main part of the file handlers, but the
files themselves are defined in the ASoC and HDA drivers with suitable
handling before calling into this shared code.

The cal_data file allows the calibration to be read and also for a
previous calibration to be written (for systems where the storage is not
something directly accessible to drivers, such as on filesystems). Code
outside the kernel should treat the content of cal_data as an opaque blob,
so the struct definition is not exported as a user API.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20251021105022.1013685-4-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>