staging: comedi: core: introduce comedi_dio_insn_config()

DIO subdevices always handle the INSN_CONFIG_DIO_{INPUT,OUTPUT} instructions
to configure the dio channels. They also always handle the INSN_CONFIG_DIO_QUERY
instruction to query the configuration of a dio channel.

Introduce a helper function to handle the (*insn_config) boilerplate for
comedi DIO subdevices. This function has the same parameters as (*insn_config)
functions with an additional parameter to allow the caller to pass a 'mask'
value for grouped dio channels.

This function returns:

  0 if the instruction was successful but requires additional handling by
  the caller (INSN_CONFIG_DIO_{INPUT,OUTPUT}

  insn->n if the instruction was handled (INSN_CONFIG_DIO_QUERY)

  -EINVAL for all unhandled instructions

The caller is responsible for actually configuring the hardware based on
the configuration (s->io_bits).

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>