dma-mapping: make support for dma ops optional

Avoid the overhead of the dma ops support for tiny builds that only
use the direct mapping.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 6fee1a1..8a45810 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -367,6 +367,7 @@
 	select ARC_PROMLIB
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_MIGHT_HAVE_PC_SERIO
+	select DMA_OPS
 	select FW_ARC
 	select FW_ARC32
 	select ARCH_MAY_HAVE_PC_FDC