staging: comedi: ni_at_ao: tidy up the register map defines

For aesthetics, sort the register map defines so the normal registers
are listed first and then alternate registers (when the GRP2WR bit is
set).

Convert the register bit defines into bit shifts to make them clear.

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>