ASoC: fsl: Drop SND_SOC_FSL_UTILS from SND_SOC_IMX_SPDIF

SND_SOC_FSL_UTILS is only used by PowerPC machines, so let's drop it in the
i.mx case.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Nicolin Chen <b42378@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>