drm/tegra: Track client version

Userspace needs to know the version of the interface implemented by a
client so it can create the proper command streams. Allow individual
drivers to store this version along with the client so that it can be
returned to userspace upon opening a channel.

Acked-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>