staging: comedi: tio: implement global tio/ctr routing

staging: comedi: tio: implement global tio/ctr routing

Adds ability to use device-global names in command args, in particular
cmd->start_arg (for NI_CtrArmStartTrigger), and cmd->scan_begin_arg or
cmd->convert_arg (either is used to specify NI_CtrGate, with preference
given to cmd->scan_begin_arg, if it is set).

The actual arguments of cmd->start_arg are not fully checked against known
register values for the particular devices because these are not documented
or currently known.  This follows the precedence of prior versions of the
tio driver.  Should these become known, they should be annotated in the
route_values tables and the set of lines in ni_tio_cmdtest should be
uncommented to allow the tests to be made.

This patch also adds interface functions that allow routes for particular
counter route destinations to be made/queried/unmade.  This allows overseer
modules to implement test_route, connect_route, and disconnect_route.  As a
part of these changes, various functions were cleaned up and clarified.

These new interface functions allow direct writing/reading of register
values.  This is an example of exactly what the new device-global access
was intended to solve:  the old interface was not consistent with other
portions of the ni_* drivers--it did not allow full register values to be
given for various MUXes.  Instead, the old interface _did_ abstract away
some of the actual hardware from the underlying devices, but it was not
consistent with any other NI hardware.  Allowing the device-global
identifiers to be used, the new patch provides for consistency across all
ni_* drivers.  One final note:  these changes provide for backwards
compatibility by allowing the older values to still be used in through the
pre-existing kernel interfaces--though not in the new device-global
test/dis/connect/route interfaces.

Signed-off-by: Spencer E. Olson <olsonse@umich.edu>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>