x86: reenable support for system without on node0

One system doesn't have RAM for node0 installed.

SRAT: PXM 0 -> APIC 0 -> Node 0
SRAT: PXM 0 -> APIC 1 -> Node 0
SRAT: PXM 1 -> APIC 2 -> Node 1
SRAT: PXM 1 -> APIC 3 -> Node 1
SRAT: Node 1 PXM 1 0-a0000
SRAT: Node 1 PXM 1 0-dd000000
SRAT: Node 1 PXM 1 0-123000000
ACPI: SLIT: nodes = 2
 10 13
 13 10
mapped APIC to ffffffffff5fb000 (        fee00000)
Bootmem setup node 1 0000000000000000-0000000123000000
  NODE_DATA [000000000000e000 - 0000000000014fff]
  bootmap [0000000000015000 -  00000000000395ff] pages 25
Could not find start_pfn for node 0
Pid: 0, comm: swapper Not tainted 2.6.24-smp-g5a514e21-dirty #14

Call Trace:
 [<ffffffff80bab498>] free_area_init_node+0x22/0x381
 [<ffffffff8045ffc5>] generic_swap+0x0/0x17
 [<ffffffff80bab0cc>] find_zone_movable_pfns_for_nodes+0x54/0x271
 [<ffffffff80baba5f>] free_area_init_nodes+0x239/0x287
 [<ffffffff80ba6311>] paging_init+0x46/0x4c
 [<ffffffff80b9dda5>] setup_arch+0x3c3/0x44e
 [<ffffffff80b978be>] start_kernel+0x6f/0x2c7
 [<ffffffff80b971cc>] _sinittext+0x1cc/0x1d3

This happens because node 0 is not online, but the node state in
mm/page_alloc.c has node 0 set.

        nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
                [N_POSSIBLE] = NODE_MASK_ALL,
                [N_ONLINE] = { { [0] = 1UL } },

So we need to clear node_online_map before initializing the memory.

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>