v4l2codecs: enumerate all possible resolutions

Some decoder may also allow to (down) scale the decoded video.
Use VIDIOC_ENUM_FRAMESIZES iotcl to enumerate the possible output
resolutions.

Part-of: <gstreamer/gst-plugins-bad!2367>
32 jobs for !2367 with v4l2codecs_enumerate_framesizes in 38 seconds (queued for 16 seconds)
latest merge request