[media] v4l2-common: add CVT and GTF detection functions

These two helper functions detect whether the analog video timings detected
by the video receiver match the VESA CVT or GTF standards.

They basically do the inverse of the CVT and GTF modeline calculations.

This patch also adds a helper function that will determine the aspect ratio
based on the provided EDID values. This aspect ratio can be given to the GTF
helper function.

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