Namelist handling of drv_flds_in when coupled to CAM

Parent for issues related to namelist handling of drv_flds_in.

When coupled to CAM BOTH CTSM or CAM can set namelist items in the shares drv_flds_in namelist. There is then checking that happens to make sure they don't conflict with each other. But in general CAM-CHEM is what should determine the setting for most of these fields. As such it makes sense to turn setting it in CTSM off when coupled to CAM.