This patch implements SMP IPIs on LEON using software generated
IRQs to signal between CPUs.

The IPI IRQ number is set by using the ipi_num property in the
device tree, or defaults to 13. LEON SMP systems should reserve
IRQ 13 (and IRQ 15) to Linux in order for the defaults to work.
Signed-off-by: NDaniel Hellstrom <daniel@gaisler.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>