locking/rtmutex: Use rt_mutex specific scheduler helpers

Have rt_mutex use the rt_mutex specific scheduler helpers to avoid
recursion vs rtlock on the PI state.

[[ peterz: adapted to new names ]]

Reported-by: Crystal Wood <swood@redhat.com>
Signed-off-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230815111430.421408298@infradead.org


Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>