ARM: SAMSUNG: Add config() function in DMA common operations

This patch adds config() that configures DMA transmit option.
This function was originally included in request(). But, Some
DMA client driver requires to change the configuration after
request(). So, This patch picks up it from request().

Signed-off-by: Boojin Kim <boojin.kim@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>