RCU pull request for v6.8

This pull request contains the following branches:

doc.2023.12.13a: Documentation and comment updates.

torture.2023.11.23a: RCU torture, locktorture updates that include
        cleanups; nolibc init build support for mips, ppc and rv64;
        testing of mid stall duration scenario and fixing fqs task
        creation conditions.

fixes.2023.12.13a: Misc fixes, most notably restricting usage of
        RCU CPU stall notifiers, to confine their usage primarily
        to debug kernels.

rcu-tasks.2023.12.12b: RCU tasks minor fixes.

srcu.2023.12.13a: lockdep annotation fix for NMI-safe accesses,
        callback advancing/acceleration cleanup and documentation
Merge branches 'doc.2023.12.13a', 'torture.2023.11.23a', 'fixes.2023.12.13a', 'rcu-tasks.2023.12.12b' and 'srcu.2023.12.13a' into rcu-merge.2023.12.13a