powerpc: Make ppc_md.{halt, restart} __noreturn

powernv marks it's halt and restart calls as __noreturn. However,
ppc_md does not have this annotation. Add the annotation to ppc_md,
and then to every halt/restart function that is missing it.

Additionally, I have verified that all of these functions do not
return. Occasionally I have added a spin loop to be sure.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/embedded6xx/mvme5100.c

@@ -177,7 +177,7 @@ static void mvme5100_show_cpuinfo(struct seq_file *m)
 	seq_puts(m, "Machine\t\t: MVME5100\n");
 }
 
-static void mvme5100_restart(char *cmd)
+static void __noreturn mvme5100_restart(char *cmd)
 {
 
 	local_irq_disable();