hw/i386/pc_piix: Move i440fx' realize near its qdev_new()

hw/i386/pc_piix: Move i440fx' realize near its qdev_new()

I440FX realization is currently mixed with PIIX3 creation. Furthermore, it is
common practice to only set properties between a device's qdev_new() and
qdev_realize(). Clean up to resolve both issues.

Since I440FX spawns a PCI bus let's also move the pci_bus initialization there.

Note that when running `qemu-system-x86_64 -M pc -S` before and after this
patch, `info mtree` in the QEMU console doesn't show any differences except that
the ordering is different.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230630073720.21297-18-shentey@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>