staging: comedi: comedi_8255: new module split from 8255

The Comedi "8255" module is both a standalone Comedi device driver
module for simple devices with one or more 8255 "Programmable Peripheral
Interface" chips at known I/O base addresses (configured at run-time),
and a helper module to configure a 8255-based digital I/O subdevice for
other Comedi drivers.

Split the "8255 subdevice helper" functionality into a new module:
"comedi_8255", leaving the standalone 8255 Comedi driver in the "8255"
module.

The Comedi "detach" routine of the standalone "8255" driver needs to
retrieve the I/O base address passed to the "comedi_8255" module to set
up each subdevice in order to release the I/O port regions it requested
in its "attach" routine.  The "comedi_8255" module stores it in a
"subdevice private" data structure that is no longer known to the "8255"
module, so add a new, exported function `subdev_8255_regbase()` to
retrieve it.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>