staging: comedi: quatech_daqp_cs: tidy up aux register bitss

For aesthetics, and use the BIT macro to define the bits and
define some macros for the timer mode and d/a update 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>