IB/qib: Remove DCA support until feature is finished

The DCA code was left over from internal development to test the
hardware feature and allow performance testing.  The results were
mixed and will require some additional work to make full use of the
feature.  Therefore, it is being removed for now.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>