[dv/lc_ctrl] lc_ctrl post M2.5 TODOs

### Description

- [x] This PR adds a new register: https://github.com/lowRISC/opentitan/pull/18302 `ext_clk_switched`.
Check this in block level.
Milestone: M3 because chip level already checked it.

- [ ] Volatile unlock enhancement 1). check otp program output won't change if it is volatile_raw_unlock transition.

- [ ] Volatile unlock enhancement 2). load otp states to rand states rather than just raw state.

- [ ] Volatile unlock enhancement 3). Support enable scb for volatile_raw_unlock.

Start with the block-level check for the ext_clk_switched work in PR 18302, then trace the lc_ctrl handling of volatile_raw_unlock and its OTP interactions. Review the three listed enhancements: preserving OTP program output, loading OTP states to random states, and enabling SCB. Done means all three behaviors are implemented and verified at block level.

Written by the indexing model from the issue text.