drm/nouveau: Document nouveau support for Tegra in DRIVER_DESC

nouveau supports the Tegra K1 and higher after the SoC-based GPUs converged
with the main GeForce GPU families.

v2:
- Qualify that support is Tegra K1+ (Martin Peres)

Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Reviewed-by: Martin Peres <martin.peres@free.fr>
Acked-by: Pierre Moreau <pierre.morrow@free.fr>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>