USB: serial: ch341: add support for GW Instek USB2.0-Serial devices

USB: serial: ch341: add support for GW Instek USB2.0-Serial devices

Programmable lab power supplies made by GW Instek, such as the
GPP-2323, have a USB port exposing a serial port to control the device.

Stringing the supplied Windows driver, references to the ch341 chip are
found. Binding the existing ch341 driver to the VID/PID of the GPP-2323
("GW Instek USB2.0-Serial" as per the USB product name) works out of the
box, communication and control is now possible.

This patch should work with any GPP series power supply due to
similarities in the product line.

Signed-off-by: Stephan Brunner <s.brunner@stephan-brunner.net>
Link: https://lore.kernel.org/r/4a47b864-0816-6f6a-efee-aa20e74bcdc6@stephan-brunner.net
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>