sparc32,sun4d: Change IPI IRQ level to prevent collision between IPI and timer interrupt

On Sun4d systems running in SMP mode, IRQ 14 is used for timer interrupts
and has a specialized interrupt handler. IPI is currently set to use IRQ 14
as well, which causes it to trigger the timer interrupt handler, and not the
IPI interrupt handler.

The IPI interrupt is therefore changed to IRQ 13, which is the highest
normally handled interrupt. This IRQ is also used for SBUS interrupts,
however there is nothing in the IPI/SBUS interrupt handlers that indicate
that they will not handle sharing the interrupt.
(IRQ 13 is indicated as audio interrupt, which is unlikely to be found in a
sun4d system)

Signed-off-by: Kjetil Oftedal <oftedal@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>