drivers: video: ov2640: migrate to Frame Interval API

[josuah]

Is your enhancement proposal related to a problem? Please describe.

#71962 introduced clock rate control, which controls the frame rate, but it uses the devicetree rather than the video API dedicated to it.

Describe the solution you'd like

Migrate the ov2640 to the Frame Interval-based API introduced in #72254 and remove the devicetree config.

Describe alternatives you've considered

Keep the devicetree for providing a default, and also introduce the API, but that is less compelling.

Additional context

#72254 got introduced after ov2640: there was no API for controlling frame rate at the time.