ASoC: pxa2xx-i2s: Fix suspend/resume

pxa2xx_i2s_resume is :
 - unconditionnaly setting SACR0_ENB
 - unsetting SACR0_ENB in saved SACR0 pxa_i2s.sacr0
fix these.

In pxa2xx_i2s_{resume,suspend}, save/restore registers even
when !dai->active.

Signed-off-by: Karl Beldan <karl.beldan@mobile-devices.fr>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>