This patch adds definitions:

  - New "video" class, for video cameras and more complicated devices;

  - New "Interface association" descriptor type, used by video class,
    along with two other assigned desciptor type codes (OTG, "debug")
    listed in the same ECN to the USB 2.0 spec;

  - Type declarations for "Interface association" and OTG descriptors.

It also replaces three copies of USB_DT_CS_* declarations in audio
support with one in <linux/usb_ch9.h>, and uses the newly exposed
symbol in "usbnet".  (Near as I can tell, the convention for those
"class specific" descriptor types started with audio, and was then
adopted by several other class specifications.)