staging: comedi: adv_pci_dio: separate out PCI-1760 support

The PCI-1760 is board unique. It uses an outgoing/incoming mailbox
programming sequence to access the hardware. The other boards supported
by this driver use simple register mapping. Including support for the
PCI-1760 in this driver just makes it harder to understand.

Separate out the PCI-1760 support into a new driver, adv_pci1760.

Clean up the new driver. The original code had a bunch of CamelCase and
other checkpatch.pl issues.

The code used to access the outgoing/incoming mailboxes was also a bit
awkward with the passing of the arrays for the outgoing and incoming
mailbox bytes. Replace them with two new functions that send a command
and return the feedback data from the command based on the programming
flow chart in the datasheet for the PCI-1760.

The new adv_pci1760 driver also fixes the incomplete timer subdevice.
This subdevice is actually the 2 PWM outputs so the subdevice type
has been changed to COMEDI_SUBD_PWM.

The counter subdevice support was not complete in the original code.
They are also a bit strange since they are up counters connected to
each of the digital inputs. For now that subdevice has been disabled
(COMEDI_SUBD_UNUSED).

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