I need to do the same - attach a MIPI camera to an i.MX6 MCU, and present a UVC interface to the USB.
I looked for UVC within the MCUXpresso peripheral configuration for the USB Middleware, and was disappointed to find this is not a supported class.
I presume this is the same functionality provided by the Ridgerun UVC Gadget Library, but $2500 license fee means I'll be dropping the iMX6 as an option for this project.
In my opinion, it's pretty ludicrous to provide a device with heavy processing power, a camera interface ideal for streaming, and then ignore the obvious STANDARD defined to complete the stream.
Cheers,
Robb.