Add GPU annotations to subroutines called from kernels

[Sergi Siso (sergisiso)]

PR Summary

Sci/Tech Reviewer:
Code Reviewer: Oakley Brunt (@oakleybrunt)

This PR has the same goal as MetOffice/lfric_core#431, to increase the coverage of LFRic code that can be offloaded to GPUs by annotating subroutines that are called from LFRic kernels but are not directly exposed to psyclone and therefore cannot be annotated automatically.

The two PRs can be merged independently, and the directives can be removed once the new build system and necessary functionality in psyclone has been added. But until then, this is the easiest practical solution to progress the work of the GIG (GPU working group).

The directives will be ignored by any compiler not targeting GPU devices.

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
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• My changes generate no new warnings
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Testing

• I have tested this change locally, using the LFRic Apps rose-stem suite
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (e.g. kgo changes)
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trac.log

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Performance Impact

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AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Documentation

• Where appropriate I have updated documentation related to this change and confirmed that it builds correctly

PSyclone Approval

• If you have edited any PSyclone-related code (e.g. PSyKAl-lite, Kernel interface, optimisation scripts, LFRic data structure code) then please contact the TCD Team

Sci/Tech Review

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• Sufficient testing has been completed

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Code Review

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• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable

[Thomas Bendall (tommbendall)]

My confusion here is why the annotations are only added to some routines and not others? For instance ffsl_flux_xy_kernel_mod.F90 is just one of several that do similar but slightly different things -- I'd expect you'd need to change all of the ffsl_flux_xy_*_kernel_mod.F90 files?