x86: fix IBM Summit based systems' phys_cpu_present_map on 32-bit kernels

x86 kernels on IBM Summit based systems will only online 1 CPU because the
phys_cpu_present_map is not set up correctly. Patch below applied to
2.6.26-git10.

Signed-off-by: Chris McDermott <lcm@linux.vnet.ibm.com>
Tested-by: Tim Pepper <lnxninga@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>