ASoC: cs53l30: Add MUTE pin control support via GPIO

The codec chip has a physical MUTE pin to let users control it via
GPIO. So this patch add a mute control support to the driver.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Acked-by: Paul Handrigan <Paul.Handrigan@cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>