x86/apic: Mop up early_per_cpu() abuse

UV X2APIC uses the per CPU variable from:

  native_smp_prepare_cpus()
    uv_system_init()
      uv_system_init_hub()

which is long after the per CPU areas have been set up.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Juergen Gross <jgross@suse.com> # Xen PV (dom0 and unpriv. guest)