[media] SDI: add flag for SDI formats and SMPTE 125M definition

Adding others generic flags, which could be used by many
components like GS1662.

Signed-off-by: Charles-Antoine Couret <charles-antoine.couret@nexvision.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>