hw/acpi: define PIIX4 acpi pci hotplug property strings at a single place

hw/acpi: define PIIX4 acpi pci hotplug property strings at a single place

Now that we have "acpi-pci-hotplug-with-bridge-support" PIIX4 PM property being
used for both q35 and i440fx machine types, it is better that we defined this
property string at a single place within a header file like other PIIX4
properties. We can then use this single definition at all the places that needs
it instead of duplicating the string everywhere. While at it, this change also
adds a definition for "acpi-root-pci-hotplug" PIIX4 PM property and uses
this definition at all places that were formally using the string value.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
Message-Id: <20210816083214.105740-1-ani@anisinha.ca>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>