ARM: tegra: document which Dalmore revisions are supported

There are a number of revisions of the Dalmore board, each with a variety
of incompatible SW-visible HW changes. The Dalmore DT file in the kernel
only supports HW revision A04. Document this in the DT file.

Reported-by: Paul Walmsley <pwalmsley@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>