xen/cpuhotplug: Replace cpu_up/down() with device_online/offline()

The core device API performs extra housekeeping bits that are missing
from directly calling cpu_up/down().

See commit a6717c01dd ("powerpc/rtas: use device model APIs and
serialization during LPM") for an example description of what might go
wrong.

This also prepares to make cpu_up/down() a private interface of the cpu
subsystem.

Signed-off-by: Qais Yousef <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

drivers/xen/cpu_hotplug.c

@@ -94,7 +94,7 @@ static int setup_cpu_watcher(struct notifier_block *notifier,
 
 	for_each_possible_cpu(cpu) {
 		if (vcpu_online(cpu) == 0) {
-			(void)cpu_down(cpu);
+			device_offline(get_cpu_device(cpu));
 			set_cpu_present(cpu, false);
 		}
 	}