xhci: Add defines for hardcoded slot states

This needs to be added to the stable trees back to 2.6.34 to support an
upcoming bug fix.

Signed-off-by: Maarten Lankhorst <m.b.lankhorst@gmail.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@kernel.org