staging: comedi: adv_pci_dio: simplify the 'boardid' boardinfo

The "board id" register is always 4-bits (4 di channels) and the register
used to read the bits is always > 0.

Simplify the 'boardid' boardinfo by replacing it with a 'id_reg' member
and open-coding the subdevice n_chan.

For aesthetics, remove all the *_BOARDID defines and just open-code the
register values in the boardinfo.

Add the missing boardinfo for the pci1739 board id register and increase
the nsubdevs to handle it.

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>