ASoC: ssm4567: Add driver for Analog Devices SSM4567 amplifier

Analog Devices SSM4567 is a boost class-D audio amplifier.

Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>