OpenACC cleanup part 1

[mlee03]

In this PR

1. New functions malloc_minmaxavg_lists and get_minmaxavg_lists are created and used to allocate and calculate values for lon_out_min_list, lon_out_max_list, lat_out_min_list, lat_out_max_list, n2_list, lon_out_avg, lon_out_list, and lat_out_list.
2. An OpenACC version of create_xgrid_2dx2d_order2 has been created and has been named as create_xgrid_2dx2d_order2_acc. This function can be found in a new file called create_xgrid_acc.c.
3. The OpenACC version create_xgrid_2dx2d_order2_acc is called in setup_conserve_interp when the _OPENACC macro is specified.
4. Data transfer OpenACC directives have been added to setup_conserve_interp.
5. Unused variables/arrays in setup_conserve_interp have been removed.