iommu/arm-smmu: program ACTLR register for qcom SMMUs

The ACTLR must be programmed according to the hardware design in order
for the coherent table walk feature to work on certain Qualcomm
hardware. Provide a new compatible string ("qcom,smmu-v2") to indicate
the relevant hardware and do the programming as needed.

Change-Id: I7e807384c821fc3d07274f35726abb28d0d75ee0
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>