powerpc/pseries: Don't try to register pseries cpu hotplug on non-pseries

This results in oddball messages at boot on other platforms telling us
that CPU hotplug isn't supported even when it is.

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/platforms/pseries/hotplug-cpu.c

···
 
 	return 0;
 }
-arch_initcall(pseries_cpu_hotplug_init);
+machine_arch_initcall(pseries, pseries_cpu_hotplug_init);