ASoC: max98090: add shutdown callback for max98090

To fix pop noise when shutdown,the pop noise during shutdown
is the pmic cutoff power of codec without any notice.

Signed-off-by: jay.xu <xjq@rock-chips.com>
Signed-off-by: zhengxing <zhengxing@rock-chips.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>