powerpc/smp: Fold cpu_die() into its only caller

Avoid the eternal confusion between cpu_die() and __cpu_die() by
removing the former, folding it into its only caller.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200819015634.1974478-2-mpe@ellerman.id.au

arch/powerpc/include/asm/smp.h

@@ -30,7 +30,6 @@ extern int spinning_secondaries;
 extern u32 *cpu_to_phys_id;
 extern bool coregroup_enabled;
 
-extern void cpu_die(void);
 extern int cpu_to_chip_id(int cpu);
 
 #ifdef CONFIG_SMP

arch/powerpc/kernel/smp.c

@@ -1492,11 +1492,7 @@ void __cpu_die(unsigned int cpu)
 void arch_cpu_idle_dead(void)
 {
 	sched_preempt_enable_no_resched();
-	cpu_die();
-}
 
-void cpu_die(void)
-{
 	/*
 	 * Disable on the down path. This will be re-enabled by
 	 * start_secondary() via start_secondary_resume() below