staging: comedi: gsc_hpdi: tidy up the register map

For aesthetics, convert the various enums into simple defines to
describe the register map for the board. Group the bit defines with
the associated register define. Convert the helper functions for
the register bit/shift/mask stuff into simple 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>