arm64: Enable CMA

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

Change-Id: I1216902a57714c85b4a7970e5c1a5dd9a1f36ab7
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>