Optimize ACC port of atm_compute_solve_diagnostics_work:7134

[abishekg7]

This PR introduces optimizations for the OpenACC port of atm_compute_solve_diagnostics_work:7134. The table below lists the timings for a real, global 30km experiment on A100 GPU with the nvhpc.

For nvhpc gpu runs, -gpu=math_uniform is introduced as a build flag to ensure optimizations are bit-identical, and the we report the numbers using NV_ACC_TIME=1. The GPU runs are on 1 Derecho GPU node, using 1 A100 via 1 MPI task.

The numbers reported for the CPU runs with gnu and intel compilers use the newly-added timers local to this region, and are averaged across three runs. The CPU runs use a single derecho CPU node each, fully subscribed to 128 MPI tasks.

Version	GPU kernel time (ms)	CPU timer - nvhpc	CPU timer - gnu	CPU timer - intel25
base	15	0.00911	0.01012	0.00901
1 Add workers	7.117	0.00911	0.01012	0.00901
2 Swap seq and vector loops	6.696	0.00941	0.01084	0.00894
3 Move efac to within vector loop	5.787	0.00997	0.01063	0.00905

This work was completed in part at the NCAR/NLR/NOAA Open Hackathon, part of the Open Hackathons program. The authors would like to acknowledge OpenACC-Standard.org for their support.