usb: xhci: Add port test modes support for usb2.

For usb2 ports, the port test mode Test_J_State, Test_K_State,
Test_Packet, Test_SE0_NAK and Test_Force_En can be enabled
as described in usb2 spec.

USB2 test mode is a required hardware feature for system integrators
validating their hardware according to USB spec, regarding signal
strength and stuff. It is purely a hardware test feature.

Usually you need an oscilloscope and have to enable those test modes on
the hardware. This will send some specific test patterns on D+/D-. There
is no report available (in Linux itself) as it is purely externally
visible. Regular USB usage is not possible at that time.
Anyone (well access to e.g. /dev/bus/usb/001/001 provided) can use it by
sending appropriate USB_PORT_FEAT_TEST requests to the hub.

[Add better commit message by Alexander Stein  -Mathias]
Signed-off-by: Guoqing Zhang <guoqing.zhang@intel.com>
Cc: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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