hw/i386/amd_iommu: Isolate AMDVI-PCI from amd-iommu device to allow full control...

hw/i386/amd_iommu: Isolate AMDVI-PCI from amd-iommu device to allow full control over the PCI device creation

Current amd-iommu model internally creates an AMDVI-PCI device. Here is
a snippet from info qtree:

  bus: main-system-bus
    type System
    dev: amd-iommu, id ""
      xtsup = false
      pci-id = ""
      intremap = "on"
      device-iotlb = false
      pt = true
    ...
    dev: q35-pcihost, id ""
      MCFG = -1 (0xffffffffffffffff)
      pci-hole64-size = 34359738368 (32 GiB)
      below-4g-mem-size = 134217728 (128 MiB)
      above-4g-mem-size = 0 (0 B)
      smm-ranges = true
      x-pci-hole64-fix = true
      x-config-reg-migration-enabled = true
      bypass-iommu = false
      bus: pcie.0
        type PCIE
        dev: AMDVI-PCI, id ""
          addr = 01.0
          romfile = ""
          romsize = 4294967295 (0xffffffff)
          rombar = -1 (0xffffffffffffffff)
          multifunction = false
          x-pcie-lnksta-dllla = true
          x-pcie-extcap-init = true
          failover_pair_id = ""
          acpi-index = 0 (0x0)
          x-pcie-err-unc-mask = true
          x-pcie-ari-nextfn-1 = false
          x-max-bounce-buffer-size = 4096 (4 KiB)
          x-pcie-ext-tag = true
          busnr = 0 (0x0)
          class Class 0806, addr 00:01.0, pci id 1022:0000 (sub 1af4:1100)
    ...

This prohibits users from specifying the PCI topology for the amd-iommu device,
which becomes a problem when trying to support VM migration since it does not
guarantee the same enumeration of AMD IOMMU device.

Therefore, allow the 'AMDVI-PCI' device to optionally be pre-created and
associated with a 'amd-iommu' device via a new 'pci-id' parameter on the
latter.

For example:
  -device AMDVI-PCI,id=iommupci0,bus=pcie.0,addr=0x05 \
  -device amd-iommu,intremap=on,pt=on,xtsup=on,pci-id=iommupci0 \

For backward-compatibility, internally create the AMDVI-PCI device if not
specified on the CLI.

Co-developed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Message-Id: <20250504170405.12623-2-suravee.suthikulpanit@amd.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>