Currently an object link property is used to pass a reference to the Heathrow
PIC into the PCI host bridge so that grackle_init_irqs() can connect the PCI
IRQs to the PIC itself.

This can be simplified by defining the PCI IRQs as qdev gpios and then wiring
up the PCI IRQs to the PIC in the Old World machine init function.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20201013114922.2946-3-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>