ASoC: max9860: switch to SPDX license tag

It's less overhead, clearer and generally neater.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Mark Brown <broonie@kernel.org>

ASoC: max9860: new driver

This is a driver for the MAX9860 Mono Audio Voice Codec.

https://datasheets.maximintegrated.com/en/ds/MAX9860.pdf

This driver does not support sidetone since the DVST register field is
backwards with the mute near the maximum level instead of the minimum.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Mark Brown <broonie@kernel.org>