RDMA/vmw_pvrdma: Use refcount_t instead of atomic_t

refcount_t is the preferred type for refcounts. Change the
QP and CQ refcnt fields to use refcount_t.

Reviewed-by: Adit Ranadive <aditr@vmware.com>
Reviewed-by: Aditya Sarwade <asarwade@vmware.com>
Reviewed-by: Jorgen Hansen <jhansen@vmware.com>
Signed-off-by: Bryan Tan <bryantan@vmware.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>