sparc/cpu: Mark cpu_play_dead() __noreturn

cpu_play_dead() doesn't return.  Annotate it as such.  By extension this
also makes arch_cpu_idle_dead() noreturn.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/847fdb53cc7124bb7c94e3e104e443a29be85184.1676358308.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

arch/sparc/include/asm/smp_64.h

@@ -49,7 +49,7 @@ int hard_smp_processor_id(void);
 
 void smp_fill_in_cpu_possible_map(void);
 void smp_fill_in_sib_core_maps(void);
-void cpu_play_dead(void);
+void __noreturn cpu_play_dead(void);
 
 void smp_fetch_global_regs(void);
 void smp_fetch_global_pmu(void);