hw/mips/malta: Set PIIX4 IRQ routes in embedded bootloader

hw/mips/malta: Set PIIX4 IRQ routes in embedded bootloader

Linux kernel expects the northbridge & southbridge chipsets
configured by the BIOS firmware. We emulate that by writing
a tiny bootloader code in write_bootloader().

Upon introduction in commit 5c2b87e34d ("PIIX4 support"),
the PIIX4 configuration space included values specific to
the Malta board.

Set the Malta-specific IRQ routing values in the embedded
bootloader, so the next commit can remove the Malta specific
bits from the PIIX4 PCI-ISA bridge and make it generic
(matching the real hardware).

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20221027204720.33611-3-philmd@linaro.org>