MIPS: loongson64: use generic dma noncoherent ops

Provide phys_to_dma/dma_to_phys helpers, everything else is generic.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Patchwork: https://patchwork.linux-mips.org/patch/19545/
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: David Daney <david.daney@cavium.com>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Tom Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: iommu@lists.linux-foundation.org
Cc: linux-mips@linux-mips.org

arch/mips/Kconfig

@@ -1828,6 +1828,7 @@ config CPU_LOONGSON2
 	select CPU_SUPPORTS_64BIT_KERNEL
 	select CPU_SUPPORTS_HIGHMEM
 	select CPU_SUPPORTS_HUGEPAGES
+	select ARCH_HAS_PHYS_TO_DMA
 
 config CPU_LOONGSON1
 	bool