CCPP-ize get_hydrostatic_energy and remove cam_thermo_formula dependency from check_energy_chng

As brought up during the review of https://github.com/ESCOMP/atmospheric_physics/pull/145 (check_energy CCPP-ization), the dependency on `cam_thermo_formula` in `check_energy_chng` run and timestep initialize:

> I'm not sure how portable the formulas for different dycores are for models beyond CAM, and this doesn't seem to be as easy to work around as the dycore_energy_consistency_adjust_run situation where a different flag could be used. I would suggest perhaps we could leave it as-is so we could CCPP-ize get_hydrostatic_energy and the corresponding formula flags in the future?