dt-bindings: arm-smmu: document the support on Milos

Add compatible for smmu representing support on the Milos SoC.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250713-sm7635-fp6-initial-v2-1-e8f9a789505b@fairphone.com


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