Add driver for DER EE DE-5000 LCR meter.

Add driver for DER EE DE-5000 LCR meter.

Add a driver for the DER EE DE-5000 LCR meter. This meter is based on
the Cyrustek ES51919/ES51920 chipset and communicates with the host
computer via an optional connectivity kit.

The kit uses an optoisolated unidirectional link to connect to the
meter and an USB cable on the host side. Internally the connection is
using the FTDI FT232R USB UART chip i.e. from the host computer point
of view the meter is connected into an RS-232 serial port.

This driver implements just a thin shim layer for registering the
driver and uses the es51919 module for all the actual work.