drivers: serial: jsm: Add the Classic board implementation

This commit adds the Digi Classic board implementation to the
staging/jsm driver.

The code here is taken from the staging/dgnc driver and modified to
match the serial/jsm state. This work is mostly based on the changes
that has been done to the code handling the Digi Neo cards with the
inspiration coming from the diff between staging/dgnc and serial/jsm
as well as the LKML history for the jsm_neo.c

The code compiles now and has no sparse and checkpatch errors or
warnings.

Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>