xtensa/cpu: Mark cpu_die() __noreturn

cpu_die() doesn't return.  Annotate it as such.  By extension this also
makes arch_cpu_idle_dead() noreturn.
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Link: https://lore.kernel.org/r/ad801544cab7c26a0f3bbf7cfefb67303f4cd866.1676358308.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

arch/xtensa/include/asm/smp.h

@@ -33,7 +33,7 @@ void show_ipi_list(struct seq_file *p, int prec);
 
 void __cpu_die(unsigned int cpu);
 int __cpu_disable(void);
-void cpu_die(void);
+void __noreturn cpu_die(void);
 void cpu_restart(void);
 
 #endif /* CONFIG_HOTPLUG_CPU */