ASoC: fsl: remove redundant Kconfig dependency on SND_SOC_POWERPC_DMA

Kconfig option SND_SOC_POWERPC_DMA is under menuconfig SND_POWERPC_SOC.
Since SND_POWERPC_SOC already depends on FSL_SOC, there is no need for
SND_SOC_POWERPC_DMA to do the same.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>