UVC driver enhancements

Since 2014 I've been working at Intel, developing software for Intel(R) RealSense(TM) UVC cameras. A small part of that work resulted in several patches to the UVC driver. So far only a small number of cosmetic patches have been merged. Several more patches, adding support for metadata nodes and asynchronous status reporting, are currently under review. Their mainlining is taking a very long time because until recently the Video4Linux subsystem had no support for camera metadata. It has only been merged in 4.12, which now allows the UVC support for metadata nodes to be merged too.