staging: lustre: o2iblnd: create union to contain FMR

staging: lustre: o2iblnd: create union to contain FMR

Create an union to contain the FMR pool structure. This is
for the preparation of adding handling Fast Registeration
support.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5783
Reviewed-on: http://review.whamcloud.com/17606
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Doug Oucharek <doug.s.oucharek@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>