PPC: E500: PCI: Make IRQ calculation more generic

The IRQ line calculation is more or less hardcoded today. Instead, let's
write it as an algorithmic function that theoretically allows an arbitrary
number of PCI slots.
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/ppce500_pci.c

@@ -253,17 +253,10 @@ static const MemoryRegionOps e500_pci_reg_ops = {
 
 static int mpc85xx_pci_map_irq(PCIDevice *pci_dev, int irq_num)
 {
-    int devno = pci_dev->devfn >> 3, ret = 0;
+    int devno = pci_dev->devfn >> 3;
+    int ret;
 
-    switch (devno) {
-        /* Two PCI slot */
-        case 0x11:
-        case 0x12:
-            ret = (irq_num + devno - 0x10) % 4;
-            break;
-        default:
-            printf("Error:%s:unknown dev number\n", __func__);
-    }
+    ret = (irq_num + devno) % 4;
 
     pci_debug("%s: devfn %x irq %d -> %d  devno:%x\n", __func__,
            pci_dev->devfn, irq_num, ret, devno);