From: William Lee Irwin III <wli@holomorphy.com>

To handle sparse physical APIC ID's properly the phys_cpu_present_map must
be scanned beyond bit NR_CPUS while ensuring no more than NR_CPUS are woken
in order not to attempt to wake non-addressible cpus.

The following patch adds that logic to smp_boot_cpus() and corrects the
failure to wake secondaries reported by dhowells, with successful wakeup,
runtime, reboot, and halting reported after it was applied.