ASoC: fsl_esai: ETDR and TX0~5 registers are non volatile

ETDR and TX0~5 registers are writable and not readable. So they are non
volatile. Remove them from volatile list, and add default register value for
them.

Signed-off-by: Zidan Wang <zidan.wang@freescale.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>