[media] tvp5150: fix s_std support

- do exact matching for special formats like PAL-M
- drop autodetect support: it's non-standard, and it is bogus as well since there
  is no way to get back the detected standard since neither g_std nor querystd are
  implemented.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>