arm64: Enable CMA

arm64 bit targets need the features CMA provides. Add the appropriate
hooks, header files, and Kconfig to allow this to happen.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --cc arch/arm64/Kconfig
Simple merge

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

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

diff --cc arch/arm64/mm/init.c
Simple merge