staging: comedi : Analog input trigerring modes for cb_pcidas

This patch allows the possibility to choose between edgre triggering
and level trigerring, for the analog input, on the Measurement
Computing PCI-DAS* boards

Signed-off-by: Brice Dubost <braice@braice.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>