southbridge/intel/bd82x6x/acpi: Fix IRQ warnings

The PCIe slot uses Message Signaled Interrupts (MSI) as the
IGD does and doesn't use hardware INT lines.
Adding the IRQ entry for PEG slot fixes a warning showing up in
GNU/Linux dmesg.

Test system:
 * Intel IvyBridge
 * Gigabyte GA-B75M-D3H

Change-Id: I5ac40e7bea9a659c6c89262aac4552bc8177a9e5
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/13612
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed