Fix race conditions with unplug/replug behavior, in particular
take care not to hold up USB probe/disconnect for long-running
framebuffer operations and rely on usb to handle teardown.

Fix for kernel panic reported with new F17 multiseat support.
Reported-by: NKay Sievers <kay.sievers@vrfy.org>
Signed-off-by: NBernie Thompson <bernie@plugable.com>