[POWERPC] PPC440EP Interrupt Triggering and Level Settings

Corrected IRQ triggering and level settings according to latest revision
of the 440EP User Manual (rev 1.24 nov 16, 2007).

The incorrect settings might cause a failure of the network if both
onchip ethernet ports are under heavy load.

Signed-off-by: Wolfgang Ocker <weo@reccoware.de>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>