acpi: x86: pcihp: add support hotplug on multifunction bridges

Commit [1] switched PCI hotplug from native to ACPI one by default.

That however breaks hotplug on following CLI that used to work:
   -nodefaults -machine q35 \
   -device pcie-root-port,id=pcie-root-port-0,multifunction=on,bus=pcie.0,addr=0x1,chassis=1 \
   -device pcie-root-port,id=pcie-root-port-1,port=0x1,addr=0x1.0x1,bus=pcie.0,chassis=2

where PCI device is hotplugged to pcie-root-port-1 with error on guest side:

  ACPI BIOS Error (bug): Could not resolve symbol [^S0B.PCNT], AE_NOT_FOUND (20201113/psargs-330)
  ACPI Error: Aborting method \_SB.PCI0.PCNT due to previous error (AE_NOT_FOUND) (20201113/psparse-531)
  ACPI Error: Aborting method \_GPE._E01 due to previous error (AE_NOT_FOUND) (20201113/psparse-531)
  ACPI Error: AE_NOT_FOUND, while evaluating GPE method [_E01] (20201113/evgpe-515)

cause is that QEMU's ACPI hotplug never supported functions other then 0
and due to bug it was generating notification entries for not described
functions.

Technically there is no reason not to describe cold-plugged bridges
(root ports) on functions other then 0, as they similarly to bridge
on function 0 are unpluggable.

So since we need to describe multifunction devices iterate over
fuctions as well. But describe only cold-plugged bridges[root ports]
on functions other than 0 as well.

1)
Fixes: 17858a16 (hw/acpi/ich9: Set ACPI PCI hot-plug as default on Q35)
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reported-by: Laurent Vivier <lvivier@redhat.com>
Message-Id: <20210723090424.2092226-1-imammedo@redhat.com>
Fixes: 17858a16 (hw/acpi/ich9: Set ACPI PCI hot-plug as default on Q35)<br>
Signed-off-by: Igor Mammedov &amp;lt;&lt;a href="mailto:imammedo@redhat.com" <target="_blank"&gt;imammedo@redhat.com&lt;/a&gt;&amp;gt;&lt;br>
Reported-by: Laurent Vivier &amp;lt;&lt;a href="mailto:lvivier@redhat.com" <target="_blank"&gt;lvivier@redhat.com&lt;/a&gt;&amp;gt;&lt;br>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>