spi: Enable SPI driver for S5P6440 and S5P6450

This patch enables the existing S3C64XX series SPI driver for S5P64X0
and removed dependency on EXPERIMENTAL because we don't need it now.

v3: Changed dependency of S3C64XX_DMA
v2: Removed dependency on EXPERIMENTAL

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Sangbeom Kim <sbkim73@samsung.com>
Acked-by: Jassi Brar <jassi.brar@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>