[crypto] Add a top attribute for checking the clkmgr jitter enable feature

PR #27673 added the capability to allow the CL checking whether the clkmgr jitter enable and other security features are enabled or disabled. Compared to other security features the clkmgr jitter feature is quite top-level specific: not every top level may have a clkmgr, and not every top-level having a clkmgr may support the feature.

To unblock other work, the current implementation just encapsulates the jitter enable check in an ifdef. Going forward this should be changed to use e.g. a top attribute as proposed by @sameo in [this comment](https://github.com/lowRISC/opentitan/pull/27673#discussion_r2478515327).