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