media: tegra-video: Enable TPG based on kernel config

Tegra internal TPG mode is only for Tegra vi and csi testing
without a real sensor and driver should default support real
sensor.

So, This patch adds CONFIG_VIDEO_TEGRA_TPG and enables Tegra
internal TPG mode only when this config is selected.

Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>