acpi_piix4: Add infrastructure to send CPU hot-plug GPE to guest

acpi_piix4: Add infrastructure to send CPU hot-plug GPE to guest

* introduce processor status bitmask visible to guest at 0xaf00 addr,
  where ACPI asl code expects it
* set bit corresponding to APIC ID in processor status bitmask on
  receiving CPU hot-plug notification
* trigger CPU hot-plug SCI, to notify guest about CPU hot-plug event

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
(cherry picked from QEMU commit b8622725cf0196f672f272922b0941dc8ba1c408)

The function piix4_cpu_hotplug_req() has been modified to take an integer
instead of a CPU object.

There was a cpu_added_notifier in the original commit, this haven't
been back-ported, as it can't be used.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>