RDMA/cxgb3: Support version 5.0 firmware

The 5.0 firmware now supports translating sgls in recv work requests,
so remove the host driver logic currently doing the translation.

Note: this change requires 5.0 firmware.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>