staging: comedi: adv_pci1710: remove 'has_large_fifo' and 'has_diff_ai' boardinfo

The pci1711/31 boards are the only ones that have a smaller FIFO (1K vs 4K) and
single-ended analog inputs (no differential).

Replace the 'has_large_fifo' and 'has_diff_ai' members of the boardinfo with
'is_pci1711' and use that to determine how to initialize the analog input
subdev_flags as well as the private data 'max_samples'.

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>