[media] tm6000: Rework standard register tables

This commit uses sentinel entries to terminate the TV standard register
tables instead of hard-coding their size, allowing further entries to be
added more easily. It is also more space-efficient if the tables have a
varying number of entries.
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>