ASoC: tas2770: Add shutdown capability via a GPIO

Add the hardware shutdown mechanism to shutdown and wake up the device
via a GPIO.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Link: https://lore.kernel.org/r/20200923132600.10652-2-dmurphy@ti.com


Signed-off-by: Mark Brown <broonie@kernel.org>