pc: acpi-build: simplify PCI bus tree generation

it basicaly does the same as original approach,
* just without bus/notify tables tracking (less obscure)
  which is easier to follow.
* drops unnecessary loops and bitmaps,
  creating devices and notification method in the same loop.
* saves us ~100LOC

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
