MSI: Use a list instead of the custom link structure

The msi descriptors are linked together with what looks a lot like
a linked list, but isn't a struct list_head list. Make it one.

The only complication is that previously we walked a list of irqs, and
got the descriptor for each with get_irq_msi(). Now we have a list of
descriptors and need to get the irq out of it, so it needs to be in the
actual struct msi_desc. We use 0 to indicate no irq is setup.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/pci/probe.c

@@ -857,6 +857,8 @@ struct pci_dev *alloc_pci_dev(void)
 	INIT_LIST_HEAD(&dev->global_list);
 	INIT_LIST_HEAD(&dev->bus_list);
 
+	pci_msi_init_pci_dev(dev);
+
 	return dev;
 }
 EXPORT_SYMBOL(alloc_pci_dev);