IB/rxe, IB/rdmavt: Use dma_virt_ops instead of duplicating it

Make the rxe and rdmavt drivers use dma_virt_ops. Update the
comments that refer to the source files removed by this patch.
Remove struct ib_dma_mapping_ops. Remove ib_device.dma_ops.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Andrew Boyer <andrew.boyer@dell.com>
Cc: Dennis Dalessandro <dennis.dalessandro@intel.com>
Cc: Jonathan Toppins <jtoppins@redhat.com>
Cc: Alex Estrin <alex.estrin@intel.com>
Cc: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>