hw/i386/pc_piix: Assign PIIX3's ISA interrupts before its realize()

hw/i386/pc_piix: Assign PIIX3's ISA interrupts before its realize()

Unlike its PIIX4 counterpart, TYPE_PIIX3_DEVICE doesn't instantiate a PIC
itself. Instead, it relies on the board to do so. This means that the board
needs to wire the ISA IRQs to the PIIX3 device model. As long as the board
assigns the ISA IRQs after PIIX3's realize(), internal devices can't be wired in
pci_piix3_realize() since the qemu_irqs are still NULL. Fix that by assigning
the ISA interrupts before realize(). This will allow for embedding child devices
into the host device as already done for PIIX4.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Message-Id: <20231007123843.127151-4-shentey@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>