arm64: Implement coherent DMA API based on swiotlb

This patch adds support for DMA API cache maintenance on SoCs without
hardware device cache coherency.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --cc arch/arm64/include/asm/cacheflush.h
Simple merge

diff --cc arch/arm64/include/asm/dma-mapping.h
Simple merge

diff --cc arch/arm64/mm/cache.S
Simple merge

diff --cc arch/arm64/mm/dma-mapping.c
Simple merge