MFC r208008

MFC r208008

 If a USB device is suspended and a USB set config request is issued when the
 USB enumeration lock is locked, then the USB stack fails to resume the device
 because locking the USB enumeration lock is part of the resume procedure. To
 solve this issue a new lock is introduced which only protects the suspend and
 resume callbacks, which can be dropped inside the usbd_do_request_flags()
 function, to allow suspend and resume during so-called enumeration operations.

git-svn-id: svn://svn.freebsd.org/base/stable/8@208221 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f