MFC r207020, r207027, r207072.

MFC r207020, r207027, r207072.

 Change usb devd events from fake attach to a notify. The ugen device is not a
 proper device_t so it faked the devctl event to appear like one, this is now a
 notify which allows more information to be passed.

 We notify for both the device attach/detach and for each usb interface. A devd
 rule can now match on the interface properties, including composite devices
 which may have a uvideo interface and also usound and possibly uhid too.

 An example to match a umass device with a scsi subclass and BBB protocol would be

 notify 100 {
 	match "system"          "USB";
 	match "subsystem"       "INTERFACE";
 	match "type"            "ATTACH";
 	match "intclass"        "0x08";
 	match "intsubclass"     "0x06";
 	match "intprotocol"     "0x50";
 	action ...
 };

 The old attach devctl event has been retained for the moment to make merging to
 8.1 easier. This was never compatible with 7.x or earlier due to the ugen regex
 change needed.

 Document the new USB notification types.

git-svn-id: svn://svn.freebsd.org/base/stable/8@207397 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f