RDMA/i40iw: Fix SD calculation for initial HMC creation

Correct SD calculation by using base address returned from commit FPM.
This alleviates any assumptions on resource ordering and alignment
requirement. Also consolidate SD estimation code into i40iw_est_sd().

Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Faisal Latif <faisal.latif@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>