x86/smp: perform disabling on interrupts ahead of AP shutdown

Move the disabling of interrupt sources so it's done ahead of the offlining
of APs.  This is to prevent AMD systems triggering "Receive accept error"
when interrupts target CPUs that are no longer online.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-Acked-by: Oleksii Kurochko<oleksii.kurochko@gmail.com>

xen/arch/x86/smp.c

@@ -374,6 +374,8 @@ void smp_send_stop(void)
         smp_call_function(stop_this_cpu, &stop_aps, 0);
 
     local_irq_disable();
+    disable_IO_APIC();
+    hpet_disable();
 
     if ( num_online_cpus() > 1 )
     {
@@ -389,8 +391,6 @@ void smp_send_stop(void)
 
     if ( cpu_online(cpu) )
     {
-        disable_IO_APIC();
-        hpet_disable();
         __stop_this_cpu();
         x2apic_enabled = (current_local_apic_mode() == APIC_MODE_X2APIC);
     }