IB/rdmavt: Create module framework and handle driver registration

This patch introduces the basics for a new module called rdma_vt. This new
driver is a software implementation of the InfiniBand verbs and aims to
replace the multiple implementations that exist and duplicate each others'
code.

While the call to actually register the device with the IB core happens in
rdma_vt, most of the work is still done in the drivers themselves. This
will be changing in a follow on patch this is just laying the groundwork
for this infrastructure.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>