staging: comedi: ni_stc.h: add some 'is_{board type}' flags to private data

The board->reg_type if checked quite often in the ni_mio_common.c code to
handle differences in the PCI devices supported by the ni_pcimio driver.
Simplify the code a bit by adding some 'is_{board type}' bit-field flags
to the private data.

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>