ARM: dts: Use generic DMA bindings for Exynos4 SPI devices

The Exynos4 SPI controller has migrated to the generic DMA bindings
since commit b5be04d3("spi: s3c64xx: Modify SPI driver to use
generic DMA DT support"). Use the generic bindings to specify the
corresponding DMA to make the SPI usable again on Exynos4x12 SoCs.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>