staging: comedi: pcl726: remove digital i/o register offsets from boardinfo

The PCL-727 board uses different register offsets for the digital input and
output ports. Instead of having all the register offsets in the boardinfo,
replace them with a simple bit-field flag, 'is_pcl727'. Use that flag in the
(*insn_bits) functions to determine what registers need to be used.

To save a bit of space, change the 'have_dio' flag in the boardinfo to a
bit-field.

For aesthetics, rename and tidy up the register map defines.

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>