amplc_dio200: Allow extra clock and gate sources for PCIe boards.

amplc_dio200: Allow extra clock and gate sources for PCIe boards.

One of the enhancements of the new PCIe boards is the addition of extra
clock and gate sources.  Allow clock and gate sources up to 31 for these
boards (compared to 7 for the old boards) although most of those are
reserved for future use.

Add constants to comedi.h for the new clock and gate sources.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>