arm64: Implement coherent DMA API based on swiotlb

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

Change-Id: I8e242d1324b017d2c080175d5f4686221c9368fc
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: b377cd6e41b8af449c10d7c2ac85f58facb42f04
Git-repo: https://git.kernel.org/cgit/linux/kernel/git/cmarinas/linux-aarch64.git


Signed-off-by: Laura Abbott <lauraa@codeaurora.org>