Surgery of the MSI interrupt handling to prepare the support of upcoming
devices which require non-PCI based MSI handling.
- Cleanup historical leftovers all over the place
- Rework the code to utilize more core functionality
- Wrap XEN PCI/MSI interrupts into an irqdomain to make irqdomain
assignment to PCI devices possible.
- Assign irqdomains to PCI devices at initialization time which allows
to utilize the full functionality of hierarchical irqdomains.
- Remove arch_.*_msi_irq() functions from X86 and utilize the irqdomain
which is assigned to the device for interrupt management.
- Make the arch_.*_msi_irq() support conditional on a config switch and
let the last few users select it.