staging/rdma/hfi1: Fix debugfs access race

Debugfs access races with the driver being ready.  Make sure the
driver is ready before debugfs files appear and debufs files are
gone before the driver starts tearing down.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>