QOM CPUState refactorings / X86CPU

* Conversion of global CPU list to QTAILQ - preparing for CPU hot-unplug
* Document X86CPU magic numbers for CPUID cache info

# gpg: Signature made Tue 03 Sep 2013 10:59:22 AM CDT using RSA key ID 3E7E013F
# gpg: Can't check signature: public key not found

# By Andreas Färber (3) and Eduardo Habkost (1)
# Via Andreas Färber
* afaerber/tags/qom-cpu-for-anthony:
  target-i386: Use #defines instead of magic numbers for CPUID cache info
  cpu: Replace qemu_for_each_cpu()
  cpu: Use QTAILQ for CPU list
  a15mpcore: Use qemu_get_cpu() for generic timers