[media] v4l2-dv-timings: add v4l2_print_dv_timings helper

Drivers often have to log the contents of a dv_timings struct. Adding
this helper will make it easier for drivers to do so.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>