dt-bindings: arm-smmu: Add compatible for SM8450 SoC

Add the SoC specific compatible for SM8450 implementing
arm,mmu-500.

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211201073943.3969549-2-vkoul@kernel.org


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