Initial driver for Korad KDxxxxP (Velleman LABPS3005D)

Initial driver for Korad KDxxxxP (Velleman LABPS3005D)

With this driver it is possible to set voltage target and current
limit. Also enabling and disabling the output is possible.

Analog output sends read back values from output. If output is
disabled analog outputs 0.00.

In protocol.c there is a g_usleep() call. This gives almost
every time enough time for PSU to parse and process input.

Multichannel devices aren't supported.