xhci: Return if xHCI doesn't support LPM

commit f0c472a6da51f9fac15e80fe2fd9c83b68754cff upstream.

Just return if xHCI is quirked to disable LPM. We can save some time
from reading registers and doing spinlocks.

Add stable tag as we want this patch together with the next one,
"Poll for U0 after disabling USB2 LPM" which fixes a suspend issue
for some USB2 LPM devices

Cc: stable@vger.kernel.org
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200624135949.22611-5-mathias.nyman@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>