linux-phytec-ti

dt-bindings: Add documentation for GM20B GPU

GM20B's definition is mostly similar to GK20A's, but requires an
additional clock.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>