staging/hfi1: Add MMU notifier callback function

TID caching will rely on the MMU notifier to be told
when memory is being invalidated. When the callback
is called, the driver will find all RcvArray entries
that span the invalidated buffer and "schedule" them
to be freed by the PSM library.

This function is currently unused and is being added
in preparation for the TID caching feature.

Signed-off-by: Mitko Haralanov <mitko.haralanov@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>