powerpc/mpc85xx: Update interrupt handling for IFC controller

IFC may have one or two interrupts.  If two interrupt specifiers are
present, the first is the "common" interrupt (CM_EVTER_STAT), and the
second is the NAND interrupt (NAND_EVTER_STAT).  If there is only one, that
interrupt reports both types of event.

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>