IB/ipath: Add code for IBA7220 send DMA

The IBA7220 HCA has a new feature to DMA data to the on chip send
buffers instead of or in addition to the host CPU doing the data
transfer.  This patch adds code to support the send DMA queue.
Signed-off-by: John Gregor <john.gregor@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>