fix: x86: support for new UV apic

Don't warn in read_apic_id() when preemptible but only one CPU online.
Signed-off-by: NAndi Kleen <andi@firstfloor.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/genapic_64.c

@@ -83,7 +83,7 @@ unsigned int read_apic_id(void)
 {
 	unsigned int id;
 
-	WARN_ON(preemptible());
+	WARN_ON(preemptible() && num_online_cpus() > 1);
 	id = apic_read(APIC_ID);
 	if (uv_system_type >= UV_X2APIC)
 		id  |= __get_cpu_var(x2apic_extra_bits);