staging: comedi: define operations for INSN_CONFIG_DIGITAL_TRIG

staging: comedi: define operations for INSN_CONFIG_DIGITAL_TRIG

The 'addi_apci_1032' driver recently started supporting the
`INSN_CONFIG_DIGITAL_TRIG` configuration instruction, but as no other
drivers were using it before, there was no existing practice of how the
instruction should look.

Define the format to be something a bit more configurable.  In
particular, a subdevice might have more than one trigger requiring an ID
and/or `COMEDI_EV_...` flags to disambiguate them, a trigger might have
more than 32 inputs, and a trigger might need several
`INSN_CONFIG_DIGITAL_TRIG` configuration instructions to configure
completely (if there are more than 32 inputs or if it uses a combination
of edge-triggered and level-triggered inputs).

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>