Instead of employing switch() statements, let's use the typical
Linux kernel idiom for handling behavioral variation: virtual
functions.

Start by defining a vector of operations for each supported memory
registration mode, and by adding a source file for each mode.
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Reviewed-by: NSagi Grimberg <sagig@mellanox.com>
Tested-by: NDevesh Sharma <Devesh.Sharma@Emulex.Com>
Tested-by: NMeghana Cheripady <Meghana.Cheripady@Emulex.Com>
Tested-by: NVeeresh U. Kokatnur <veereshuk@chelsio.com>
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>