edid: add support for CVT timing code descriptors

The problem here is mostly if/how we want to reuse the CVT definitions from the range limit.

The VESA EDID Video Timing Block Extension also reuses the Detailed Timing Block (DTB) Descriptors, Coordinated Video Timing (CVT) Descriptors, and Standard Timing (ST) Descriptors. So we might want to move all of that to some common location.

depends on !114 (merged)