dt-bindings: arm-smmu: Add compatible string for Adreno GPU SMMU

Every Qcom Adreno GPU has an embedded SMMU for its own use. These
devices depend on unique features such as split pagetables,
different stall/halt requirements and other settings. Identify them
with a compatible string so that they can be identified in the
arm-smmu implementation specific code.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20201109184728.2463097-4-jcrouse@codeaurora.org


Signed-off-by: Will Deacon <will@kernel.org>