hw/mips/gt64xxx_pci: Fix PCI IRQ levels to be preserved during migration

hw/mips/gt64xxx_pci: Fix PCI IRQ levels to be preserved during migration

Based on commit e735b55a8c11dd455e31ccd4420e6c9485191d0c:

  piix_pci: eliminate PIIX3State::pci_irq_levels

  PIIX3State::pci_irq_levels are redundant which is already tracked by
  PCIBus layer. So eliminate them.

The IRQ levels in the PCIBus layer are already preserved during
migration. By reusing them and rather than having a redundant implementation
the bug is avoided in the first place.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20220217101924.15347-2-shentey@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>