[SPARC64]: Consolidate MSI support code.

This also makes us use the MSI queues correctly.

Each MSI queue is serviced by a normal sun4u/sun4v INO interrupt
handler.  This handler runs the MSI queue and dispatches the
virtual interrupts indicated by arriving MSIs in that MSI queue.

All of the common logic is placed in pci_msi.c, with callbacks to
handle the PCI controller specific aspects of the operations.

This common infrastructure will make it much easier to add MSG
support.

Signed-off-by: David S. Miller <davem@davemloft.net>