V4L/DVB (13913): saa7127: Add support for generating SECAM output for the SAA712...

This change fixes up saa7127_s_std() generate SECAM out, if the user has
requested a 50 Hz video standard set that only contains a request for SECAM
standards and not PAL.  Only the SAA712[89] chips can generate SECAM, the
SAA712[67] chips cannot.

I was unclear on the burst start and end values - I couldn't figure out
the units - so I left them the same as for the PAL systems.

A the video decoders on both a PVR-350 (SAA7115) and an HVR-1600 (CX23418)
identify the SECAM signal generated by a SAA7129 with this patch as SECAM.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>