xhci: Show ZHAOXIN xHCI root hub speed correctly

Some ZHAOXIN xHCI controllers follow usb3.1 spec, but only support
gen1 speed 5Gbps. While in Linux kernel, if xHCI suspport usb3.1,
root hub speed will show on 10Gbps.
To fix this issue of ZHAOXIN xHCI platforms, read usb speed ID
supported by xHCI to determine root hub speed. And add a quirk
XHCI_ZHAOXIN_HOST for this issue.

[fix warning about uninitialized symbol -Mathias]

Suggested-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Weitao Wang <WeitaoWang-oc@zhaoxin.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Message-ID: <20230602144009.1225632-11-mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>