USB: usbserial: mos7720: add support for parallel port on moschip 7715

Add support for the parallel port on the moschip MCS7715 device.  The port
registers itself with the parport subsystem as a low-level driver.  A separate
entry to the kernel configuration is added beneath that for the mos7720, to
avoid the need to link with the parport subsystem code for users who don't have
or don't want the parallel port.  Only compatibility mode is currently supported
(no ECP/EPP).  Tested with both moschip devices (7720 and 7715) on UP and SMP
hosts, including regression testing of serial port, concurrent operation of
serial and parallel ports, and various connect / disconnect scenarios.

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>