RTEMS | rtems: Fix the counter conversion overflows (!1526)

[Sebastian Huber (@sebhub)]

Sebastian Huber created a merge request: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1526

Project:Branches: sebhub/rtems:up/counter-conversion to rtems/rtos/rtems:main
Author: Sebastian Huber

## Summary

Issue #5806: The counter conversions overflow above a few seconds

Compute the 96-bit product of the counter ticks and the scaler from two
32-bit by 32-bit products.  The result is the same as before for each
value which did not overflow.  `spcpucounter01` checks the conversions
at three seconds and at the maximum counter ticks.

With the old converter, `spcpucounter01` fails on Qemu `xlnx-zcu102`.
With the fix, it passes.

**BSP** `aarch64/zynqmp_apu` · **Simulator** Qemu, `-machine xlnx-zcu102`

## AI Details
<!-- Make sure you have read our statement at https://www.rtems.org/generative-ai/ -->

### Prompt used

None as a single prompt.  The work was done in an interactive Claude Code
session on the RTEMS tree.  The task was to find why the test framework
reported a too short duration for a long performance test run, and to
fix the cause.  Each change was directed and reviewed.

### AI model used

Claude Opus 5.5 (claude-opus-5-5), through Claude Code.

### How AI was used for the contribution

- ( ) Formatting
- (x) Test creation.
- (x) Code comments.
- ( ) The entire contribution was generated using AI
- ( ) AI code completion such as Copilot in VSCode.

The diagnosis, the test and the implementation were produced in that
session under my direction, and the commit message was drafted there.

### Access

I have not used a product which claims copyright in its output, and I have
legitimate access to the one I used.

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1526
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