mips/cpu: Mark play_dead() __noreturn

play_dead() doesn't return.  Annotate it as such.  By extension this
also makes arch_cpu_idle_dead() noreturn.
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/2897b51a9b8beb5b594fe66fb1d3a479ddd2a0e2.1676358308.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

arch/mips/include/asm/smp.h

@@ -88,7 +88,7 @@ static inline void __cpu_die(unsigned int cpu)
 	mp_ops->cpu_die(cpu);
 }
 
-extern void play_dead(void);
+extern void __noreturn play_dead(void);
 #endif
 
 #ifdef CONFIG_KEXEC