x86: fix memoryless node oops during boot

fix oops during boot reported in this thread:

  http://lkml.org/lkml/2008/2/6/65

enable booting on memoryless nodes.

Reported-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>