Remove arch_is_coherent() from iommu dma ops and implement separate
coherent ops functions.
Signed-off-by: Rob Herring <rob.herring@calxeda.com> Cc: Russell King <linux@arm.linux.org.uk> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>