x86, numa: Fix numa_emulation code with memory-less node0

This crash happens on a system that does not have RAM on node0.

When numa_emulation is compiled in, and:

 1. we boot the system without numa=fake...
 2. or we boot the system with numa=fake=128 to make emulation fail

we will get:

[    0.076025] ------------[ cut here ]------------
[    0.080004] kernel BUG at arch/x86/mm/numa_64.c:788!
[    0.080004] invalid opcode: 0000 [#1] SMP
[...]

need to use early_cpu_to_node() directly, because cpu_to_apicid
and apicid_to_node will return node0 that is not onlined.
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
LKML-Reference: <4D6ECF72.5010308@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/numa_64.c

@@ -780,11 +780,7 @@ void __cpuinit numa_add_cpu(int cpu)
 	int physnid;
 	int nid = NUMA_NO_NODE;
 
-	apicid = early_per_cpu(x86_cpu_to_apicid, cpu);
-	if (apicid != BAD_APICID)
-		nid = apicid_to_node[apicid];
-	if (nid == NUMA_NO_NODE)
-		nid = early_cpu_to_node(cpu);
+	nid = early_cpu_to_node(cpu);
 	BUG_ON(nid == NUMA_NO_NODE || !node_online(nid));
 
 	/*