Add ndep to one of the histaux_atm2med lists

[billsacks]

Now that ndep is always being sent from CAM in CESM, we need to add it to one of the histaux_atm2med lists in namelist_definition_drv.xml. In talking with @olyson we're not sure which list is most appropriate: the 3-hourly list or the 24-hourly list. The 24-hourly list contains other deposition fields, so that might be the most appropriate, unless there is important diurnal variability in N deposition that needs to be captured.