Add mixed mode support to use in AM5

[uramirez8707]

Description
Adds mixed mode support for fv3 to be used in AM5 (i.e compile fv3 with r4 and the rest with r8)

The following subroutines were updated to accept r4 and r8 arguments:

• atmosphere_boundary
• atmosphere_pref
• atmosphere_cell_area
• get_bottom_mass
• get_bottom_wind
• get_stock_pe

This was done using the #include method to be consistent with FMS. This was needed because they are called from atmos_drivers.

If compiling with r4, the r4 version of fms constants is used.

Fixes # (issue)

How Has This Been Tested?
AM5 was ran in mixed mode

Checklist:

Please check all whether they apply or not

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[lharris4]

Approved. Nice use of templating to avoid redundant code.