Realtime preemption locking core merged

The 5.15 merge window is off to a fast start; stay tuned for our usual fullsummary. It is worth mentioning, though, that the realtime preemptionlocking code has been pulled into themainline with little fanfare. This work began in 2004 and has fundamentallychanged many parts of the core kernel. With this pull, the sleepable locksthat make deterministic realtime response possible have finally joined allof that other work (though the kernel must be built with theREALTIME configuration option to use them).

Congratulations are due to all of the realtime developers who pushed thisproject forward for nearly two decades.