v4l2videodec: Implement profile/level enumeration

Submitted by Nicolas Dufresne @ndufresne

Link to original bug (#797053)

Description

The profile/level controls are using the menu type, so that driver can list the subset of the profile/level they support.

GStreamer is missing code that enumerate the supported value and use that to limit which profiles/level are supported. Fixing this will allow rejecting in playbin/decodebin the HW decoder when a specific profile/level isn't supported by the HW.