Silence the following warnings when built with W=1:
| CC drivers/acpi/acpi_processor.c
| warning: no previous prototype for 'arch_register_cpu' [-Wmissing-prototypes]
| int __weak arch_register_cpu(int cpu)
| ^
| CC drivers/acpi/acpi_processor.c
| warning: no previous prototype for 'arch_unregister_cpu' [-Wmissing-prototypes]
| void __weak arch_unregister_cpu(int cpu) {}
| ^
Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>