dma-mapping: merge direct and noncoherent ops

All the cache maintainance is already stubbed out when not enabled,
but merging the two allows us to nicely handle the case where
cache maintainance is required for some devices, but not others.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Paul Burton <paul.burton@mips.com> # MIPS parts
diff --git a/arch/nds32/Kconfig b/arch/nds32/Kconfig
index 7068f34..5699233 100644
--- a/arch/nds32/Kconfig
+++ b/arch/nds32/Kconfig
@@ -11,7 +11,7 @@
 	select CLKSRC_MMIO
 	select CLONE_BACKWARDS
 	select COMMON_CLK
-	select DMA_NONCOHERENT_OPS
+	select DMA_DIRECT_OPS
 	select GENERIC_ATOMIC64
 	select GENERIC_CPU_DEVICES
 	select GENERIC_CLOCKEVENTS