xHCI: Check host USB2 LPM capability

Check the host's USB2 LPM capability.

USB2 software LPM support is optional for xHCI 0.96 hosts. xHCI 1.0 hosts
should support software LPM, and may support hardware LPM.

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