omap: IOMMU: add support to callback during fault handling

Add support to register an isr for IOMMU fault situations and adapt it
to allow such (*isr)() to be used as fault callback. Drivers using IOMMU
module might want to be informed when errors happen in order to debug it
or react.

Signed-off-by: David Cohen <dacohen@gmail.com>
Acked-by: Hiroshi DOYU <Hiroshi.DOYU@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>