CVE-2023-54267 powerpc/pseries: Rework lppaca_shared_proc() to avoid DEBUG_PREEMPT

In the Linux kernel, the following vulnerability has been resolved: powerpc/pseries: Rework lppacasharedproc to avoid DEBUGPREEMPT lppacasharedproc takes a pointer to the lppaca which is typically accessed through getlppaca. With DEBUGPREEMPT enabled, this leads to checking if preemption is...