ASoC: cs35l56: Allow restoring factory calibration through ALSA control

ASoC: cs35l56: Allow restoring factory calibration through ALSA control

Add an ALSA control (CAL_DATA) that can be used to restore amp calibration,
instead of using debugfs. A readback control (CAL_DATA_RB) is also added
for factory testing.

On ChromeOS the process that restores amp calibration from NVRAM has
limited permissions and cannot access debugfs. It requires an ALSA control
that it can write the calibration blob into. ChromeOS also restricts access
to ALSA controls, which avoids the risk of accidental or malicious
overwriting of good calibration data with bad data. As this control is not
needed for normal Linux-based distros it is a Kconfig option.

A separate control, CAL_DATA_RB, provides a readback of the current
calibration data, which could be either from a write to CAL_DATA or the
result of factory production-line calibration.

The write and read are intentionally separate controls to defeat "dumb"
save-and-restore tools like alsa-restore that assume it is safe to save
all control values and write them back in any order at some undefined
future time. Such behavior carries the risk of restoring stale or bad data
over the top of good data.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20251111130850.513969-3-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>