spi/s3c64xx: Add support DMA engine API

This patch adds to support DMA generic API to transfer raw
SPI data. Basiclly the spi driver uses DMA generic API if
architecture supports it. Otherwise, uses Samsung specific
S3C-PL330 APIs.

Signed-off-by: Boojin Kim <boojin.kim@samsung.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>