media: Kconfig: mark other drivers as test drivers

Neither the PCI skeleton nor the DVB dummy driver are real
drivers. They're there just as an example for a driver
writter.

Distros should not enable those drivers. So, hide them if
MEDIA_TEST_SUPPORT is not selected.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>