IB/hfi1: Move QOS decision logic into its own function

The decision to use QOS affects other resource allocation.
Move the QOS decision logic into its own function so it can
be called by other interested parties.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>