USB: xhci: Respect critical sections.

Narrow down time spent holding the xHCI spinlock so that it's only used to
protect the xHCI rings, not as mutual exclusion.  Stop allocating memory
while holding the spinlock and calling xhci_alloc_virt_device() and
xhci_endpoint_init().

The USB core should have locking in it to prevent device state to be
manipulated by more than one kernel thread.  E.g. you can't free a device
while you're in the middle of setting a new configuration.  So removing
the locks from the sections where xhci_alloc_dev() and
xhci_reset_bandwidth() touch xHCI's representation of the device should be
OK.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>