powerpc/fsl_rio: Error interrupt handler for sRIO on MPC85xx

The sRIO controller reports errors to the core with one signal, it uses
register EPWISR to provides the core quick access to where the error
occurred.  The EPWISR indicates that there are 4 interrupts sources,
port1, port2, message unit and port write receive, but the sRIO driver
does not support port2 for now, still the handler takes care of port2.
Currently the handler only clear error status without any recovery.

Signed-off-by: Shaohui Xie <b21989@freescale.com>
Cc: Li Yang <leoli@freescale.com>
Cc: Kumar Gala <kumar.gala@freescale.com>
Cc: Roy Zang <tie-fei.zang@freescale.com>
Cc: Alexandre Bounine <alexandre.bounine@idt.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>