x86/PCI: Handle PIRQ routing tables with no router device given

PIRQ routing tables provided by the PCI BIOS usually specify the PCI 
vendor:device ID as well as the bus address of the device implementing 
the PIRQ router, e.g.:

PCI: Interrupt Routing Table found at 0xc00fde10
[...]
PCI: Attempting to find IRQ router for [8086:7000]
pci 0000:00:07.0: PIIX/ICH IRQ router [8086:7000]

however in some cases they do not, in which case we fail to match the 
router handler, e.g.:

PCI: Interrupt Routing Table found at 0xc00fdae0
[...]
PCI: Attempting to find IRQ router for [0000:0000]
PCI: Interrupt router not found at 00:00

This is because we always match the vendor:device ID and the bus address 
literally, even if they are all zeros.

Handle this case then and iterate over all PCI devices until we find a 
matching router handler if the vendor ID given by the routing table is 
the invalid value of zero:

PCI: Attempting to find IRQ router for [0000:0000]
PCI: Trying IRQ router for [1039:0496]
pci 0000:00:05.0: SiS85C497 IRQ router [1039:0496]

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nikolai Zhubr <zhubr.2@gmail.com>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2203302018570.9038@angie.orcam.me.uk