stm32u5: Re-implement VCO input and EPOD configuration

[erwango]

Describe the bug
During implementation of #41310, VCO input and EPOD configuration were removed.
Initial tests didn't show any adverse effect, but it would be saner to re-instantiate this piece of code.

Instead of doing it directly in #41310, it is proposed to do it on top of #41585,
taking benefit of tests and code optimization provided.

[erwango]

@ABOSTM fyi

[github-actions]

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[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.