ASoC: SAMSUNG: Clean-up DMA header file

This patch moves DMA specific definitions, they doesn't need to be
shared, into 'dma.c' from 'dma.h'. And remove unnecessery definitions
on 'dma.h'.

Signed-off-by: Seungwhan Youn <sw.youn@samsung.com>
Acked-by: Jassi Brar <jassi.brar@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>