IB/hfi1: Allow the driver to initialize QP priv struct

This patch adds an interface to allow the driver to initialize the QP priv
struct when the QP is created and after the qpn has been assigned.  A
field is added to the QP priv struct to reference the rcd and two new
files are added to contain the function to initialize the rcd field so
that more TID RDMA related code can be added here later.

Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>