Initialize and power the 3D unit on Tegra20, Tegra30 and Tegra114 and
register a channel with the Tegra DRM driver so that the unit can be
used from userspace.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>