seabios q35: Add new PCI slot to irq routing function

seabios q35: Add new PCI slot to irq routing function

q35/ich9 doesn't use the same interrupt mapping function as
i440fx/piix.  PIRQA:D and PIRQE:H are programmed identically, but we
start at index 0, not index -1.  Slots 25 through 31 are also
programmed independently.

When running qemu w/o this patch, a device at address 0:6.0 will have
its PCI interrupt line register programmed with irq 10 (as seen by
info pci), but it actually uses irq 11 (as reported the guest).  Half
of the interrupt lines are misprogrammedi like this.  Functionally, a
fully emulated qemu guest doesn't care much, but when we try to use
device assignment, we really need to know the correct irqs.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>