sparc32,leon: implement genirq CPU affinity

A simple implementation of CPU affinity, the first CPU in
the affinity CPU mask always takes the IRQ.

Signed-off-by: Daniel Hellstrom <daniel@gaisler.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>