lib/smp_processor_id: Move it into noinstr section

That code is already not traceable. Move it into the noinstr section so the
objtool section validation does not trigger.

Annotate the warning code as "safe". While it might be not under all
circumstances, getting the information out is important enough.

Should this ever trigger from the sensitive code which is shielded against
instrumentation, e.g. low level entry, then the printk is the least of the
worries.

Addresses the objtool warnings:
 vmlinux.o: warning: objtool: context_tracking_recursion_enter()+0x7: call to __this_cpu_preempt_check() leaves .noinstr.text section
 vmlinux.o: warning: objtool: __context_tracking_exit()+0x17: call to __this_cpu_preempt_check() leaves .noinstr.text section
 vmlinux.o: warning: objtool: __context_tracking_enter()+0x2a: call to __this_cpu_preempt_check() leaves .noinstr.text section

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134340.902709267@linutronix.de