x86: initialize memnodemapsize while faking NUMA node

When system turns NUMA off or system lacks of NUMA support,
Xen will fake a NUMA node to make system works as a single
node NUMA system.

In this case the memory node map doesn't need to be allocated
from boot pages, it will use the _memnodemap directly. But
memnodemapsize hasn't been set. Xen should assert in phys_to_nid.
Because x86 was using an empty macro "VIRTUAL_BUG_ON" to replace
ASSERT, this bug will not be triggered on x86.

Actually, Xen will only use 1 slot of memnodemap in this case.
So we set memnodemap[0] to 0 and memnodemapsize to 1 in this
patch to fix it.

Signed-off-by: Wei Chen <wei.chen@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/numa.c

@@ -270,6 +270,10 @@ void __init numa_initmem_init(unsigned long start_pfn, unsigned long end_pfn)
     /* setup dummy node covering all memory */
     memnode_shift = BITS_PER_LONG - 1;
     memnodemap = _memnodemap;
+    /* Dummy node only uses 1 slot in reality */
+    memnodemap[0] = 0;
+    memnodemapsize = 1;
+
     nodes_clear(node_online_map);
     node_set_online(0);
     for ( i = 0; i < nr_cpu_ids; i++ )