[ACPI] pci-irq routing v.4: clean up acpi_pci_[link,root]

[Dominik B. <de...@br...>]

v.4:
x add acpi_pci_get_link_for_dev() to acpi_pci_root.c
x this makes acpi_prt_get_irq, acpi_prt_set_irq, acpi_pci_link_set_irq
	and acpi_pci_link_get_irq unnecessary ("sanity checks" were
	moved, of course)
x improved validation

v.3:
x Move prt_set_irq and eisa_set_level-workaround to pci_acpi_assign_irq
x Actually perform (at least one step of) the validation in
	pci_acpi_validate_irq
x make clear what's left <TBD>
x always exit pci_acpi_-functions when a working IO_APIC is found.

v.2:
x do not break second pci_for_each_dev - run
x move io_apic_assign to an extra function - makes the code a lot cleaner
x check for "pin 0" which means the PCI dev doesn't need an IRQ.

v.1:
x move acpi-related code out of pcibios_lookup_irq
x add 3-step ACPI PCI-IRQ routing initialization


Next steps would be moving the PCI Link enabling to pci_acpi_assign_irq, and 
adding the balancing code.

Patch is against plain acpi-20020404 / Kernel 2.5.8-pre3, as usual.

Dominik