Unify reduced complexity mode namelist selection

[glemieux]

Describe the changes

Instead of the user setting reduced complexity mode options individually, have them select a string option for a single namelist mode variable. For example in the namelist definition file:

<entry id="fates_complexity_mode" type="char*256" category="physics"
        group="clm_inparm" valid_values="full_complexity, nocomp, fixedbiogeo, ncfbg, satphen, st3, pphys">
Set FATES reduced complexity mode by setting fates_complexity_mode to a valid string option.
</entry>

Is your request related to a problem?

Incorporating this would help to address #1356.

Alternative options

No response

Additional context

No response

[glemieux]

Per discussion during fates software meeting today, we should remove pphys out of the is as it is theoretically possible that it could be used with reduced complexity modes.

[ekluzek]

This a much clearer and user friendly way to do this. And it can also improve the code and make error checking easier.