staging: media: tegra-video: add a per-soc enable/disable op

The Tegra20 VI needs an additional operation to enable the VI, add an
operation for that.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>