sparc32, sun4d: Implemented SMP IPIs support for SUN4D machines

The sun4d does not seem to have a distingstion between soft and hard
IRQs. When generating IPIs the generated IRQ looks like a hard IRQ,
this patch adds a "IPI check" in the sun4d irq trap handler at a
predefined IRQ number (SUN4D_IPI_IRQ). Before generating an IPI
a per-cpu memory structure is modified for the "IPI check" to
successfully detect a IPI request to a specific processor, the check
clears the IPI work requested.

All three IPIs (resched, single and cpu-mask) use the same IRQ
number.

The IPI IRQ should preferrably be on a separate IRQ and definitly
not shared with IRQ handlers requesting IRQ with IRQF_SHARED.

Signed-off-by: Daniel Hellstrom <daniel@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>