ASoC: fsi: add valid data position control support

FSI2 can control valid data position, like
package in front/back or stream  mode (16bit x 2).
But current fsi driver is assuming it was in-back.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>