From: James Cleverdon <jamesclv@us.ibm.com>

In forthcoming IBM x445 systems, the physical APIC ID will not follow the
simple rule laid out by Intel and encoded into xapic_phys_to_log_apicid.
(The BIOS code that sets IDs doesn't work right above 16 CPUs if HT is turned 
on, so for > 16-way the BIOS will disable HT and repack the physical CPUs
into APIC clusters.)

Anyway, it's a good idea to make the APIC code more independent of any
particular BIOS numbering scheme.  This patch allocates logical IDs based on
how many CPUs have already been onlined in a particular APIC cluster.