This removes the acpi_irq_balance_set() interface from the PCI
interrupt link driver.

x86 used acpi_irq_balance_set() to tell the PCI interrupt link
driver to configure links to minimize IRQ sharing.  But the link
driver can easily figure out whether to turn on IRQ balancing
based on the IRQ model (PIC/IOAPIC/etc), so we can get rid of
that external interface.

It's better for the driver to figure this out at init-time.  If
we set it externally via the x86 code, the interface reduces
modularity, and we depend on the fact that acpi_process_madt()
happens before we process the kernel command line.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>