The ssm2305 is a simple Class-D audio amplifier. A application can
turn on/off the device by a gpio. It's also possible to hardwire the
shutdown pin.

Tested on a i.MX6 based custom board.
Signed-off-by: NMarco Felsch <m.felsch@pengutronix.de>
Reviewed-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NMark Brown <broonie@kernel.org>