dt-bindings: iommu: dart: add t6000 compatible

The M1 Max/Pro SoCs come with a new DART variant that is incompatible with
the previous one. Add a new compatible for those.

Signed-off-by: Sven Peter <sven@svenpeter.dev>
Acked-by: Rob Herring <robh@kernel.org>

Signed-off-by: Janne Grunau <j@jannau.net>
Signed-off-by: Hector Martin <marcan@marcan.st>