staging: comedi: ni_mio_common: implement new routing for TRIG_EXT

staging: comedi: ni_mio_common: implement new routing for TRIG_EXT

Use new signal routing capability for all comedi command *_src == TRIG_EXT
options.  This new interface allows the user specify signals and terminals
as TRIG_EXT sources using a very consistent naming convention. Furthermore,
the interface allows backwards compatibility to prior behavior of
specifying register-level (or near register-level) values as *_arg options
when *_src == TRIG_EXT.

Annotates and updates tables of register values to reflect this new
implementation status.

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>