spi: s3c64xx: Do not use platform_data for DMA parameters

All related platforms use either devicetree or the DMA slave
map API for mapping DMA channels to DMA slaves so we can now
stop using platform_data for passing DMA details.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Tested-by: Andi Shyti <andi.shyti@samsung.com>
Tested-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>