ASoC: pxa2xx-i2s: Handle SACR1_DRPL and SACR1_DREC separately

- hw_params enables both RPL and REC functions each time : Enable the
	appropriate function in pxa2xx_i2s_trigger.
- pxa2xx_i2s_shutdown disables i2s anytime one of RPL or REC function is
	off : Turn it off only when both functions are off.

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