spi: s3c64xx: Modify SPI driver to use generic DMA DT support

This patch modifies the SPI driver to use generic dma dt bindings
support. This passes all the required arguments to dma dev request
functon which in turn calls the dma_request_slave_channel or dma__
request_channel based on DT or non-DT respectively.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>