staging: media: tegra-video: add H/V flip controls

Tegra20 can do horizontal and vertical image flip, but Tegra210 cannot
(either the hardware, or this driver).

In preparation to adding Tegra20 support, add a flag in struct tegra_vi_soc
so the generic vi.c code knows whether the flip controls should be added or
not.

Also provide a generic implementation that simply sets two flags in the
channel struct. The Tegra20 implementation will enable flipping at stream
start based on those flags.

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>