x86/PCI: Fix ALi M1487 (IBC) PIRQ router link value interpretation

Fix an issue with commit 1ce849c7 ("x86/PCI: Add support for the ALi 
M1487 (IBC) PIRQ router") and correct ALi M1487 (IBC) PIRQ router link 
value (`pirq' cookie) interpretation according to findings in the BIOS.

Credit to Nikolai Zhubr for the detective work as to the bit layout.

Fixes: 1ce849c7 ("x86/PCI: Add support for the ALi M1487 (IBC) PIRQ router")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2203310013270.44113@angie.orcam.me.uk