qemu: capablities: detect presence of acpi-root-pci-hotplug for i440fx machines

qemu: capablities: detect presence of acpi-root-pci-hotplug for i440fx machines

The following change in qemu added support for a global boolean flag specific
to i440fx machines that would turn off or on acpi based hotplug for pci root
bus:

3d7e78aa7777f ("Introduce a new flag for i440fx to disable PCI hotplug on the root bus")

The option is passed as "-global PIIX4_PM.acpi-root-pci-hotplug=on" etc in qemu
commandline. It is enabled by default. This patch adds the corresponding qemu
capabilities in libvirt as QEMU_CAPS_PIIX_ACPI_ROOT_PCI_HOTPLUG.

Please note that the test specific qemu capabilities .replies files has already
been updated as a part of regular refreshing them when a new qemu version is
released. Hence, no updates to those files are required.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
Reviewed-by: Laine Stump <laine@redhat.com>