staging: comedi: comedi_fc.h: begin migration to comedidev.h

"comedi_fc.h" contains a few inline functions used by the `do_cmdtest`
handler functions for comedi subdevices in several low-level comedi
drivers for checking asynchronous command trigger sources and arguments.
They all use the prefix `cfc_check_trigger_arg`.  Copy them over to
"../comedidev.h", but change the `cfc_` prefix to `comedi_`.  Change the
original functions in "comedi_fc.h" into simple wrappers for their
replacements.

Once the drivers have been changed to call the replacement functions,
"comedi_fc.h" can be removed.

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>