xHCI: Clear PLC in xhci_bus_resume()

This patch clears PORT_PLC if xhci_bus_resume() resumes a previous suspended
port, because if a port transition from U3 to U0 state, it will report a
port link state change, and software should clear the corresponding PLC bit.

It also uses hcd->speed to check if a port is a USB2 protocol port.

The patch fixes the issue that USB keyboard can not wakeup system from
hibernation.

Signed-off-by: Andiry Xu <andiry.xu@amd.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>