pc: Delay setting number of boot CPUs to machine_done time

pc: Delay setting number of boot CPUs to machine_done time

Currently present CPUs counter in CMOS only contains
smp_cpus (i.e. initial CPUs specified with -smp X) and
doesn't account for CPUs created with -device.
If VM is started with additional CPUs added with
 -device, it will hang in BIOS waiting for condition
   smp_cpus == counted_cpus
forever as counted_cpus will include -device CPUs as well
and be more than smp_cpus.

Make present CPUs counter in CMOS to count all CPUs
(initial and coldplugged with -device) by delaying
it to machine done time when it possible to count
CPUs added with -device.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>