staging/rdma/hfi1: Determine actual operational VLs

Use shared credits and dedicated credits for each VL to determine
the actual number of operational VLs.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>