media: atomisp: Remove test pattern generator (TPG) support

The TPG support registers a v4l2-subdev for this, but this is not part of
the media-controller graph in any way. After manually selecting the TPG
as input using the s_input ioctl it does not work.

Several supported sensors have their own working TPG and using the sensor's
TPG means that the same data-flow is used as with actual sensors rather
then the quite different data-flow from the ISP's builtin TPG.

Remove the broken TPG support, when a test-pattern is needed for testing
a sensor's TPG can be used. Using a sensor's TPG is actually better for
testing since then the actual normal data-flow is being tested.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>