8250_pci: improve code comments and Kconfig help

The recent regression about NetMos 9835 Multi-I/O boards indicates
that comment pointing to the parport_serial driver could be helpful.

Signed-off-by: Stefan Seyfried <seife+kernel@b1-systems.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>