Enable GPU execution of loops in atm_srk3 involving module level variables

[abishekg7]

This PR ports some of the loops in the mpas_atm_time_integration and mpas_atm_core modules, which initialize module level variables belonging to the mpas_atm_time_integration module, to OpenACC in preparation for the consolidating all data transfers between host and device to before and after each dynamics call.

In order to do this, we also declare the allocatable module level variables in this scope using the OpenACC declare create statement, which instructs the nvhpc compiler to automatically create and delete the variable whenever it encounters an allocate or deallocate statement, respectively. This commit also removes these variables from manual data movement statements as required.

This PR also introduces some integers for loop bounds, so as to dereference scalar integer pointers which the OpenACC parallel regions do not correctly copy to device memory in the presence of a default(present) clause.