IB/hfi1: Unify access to GUID entries

This patch consolidates the node GUIDs and the port GUID handling
and unifies access to these items. The knowledge of hfi1 GUIDs'
design and their location are kept in accessors to centralize access.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Brian Welty <brian.welty@intel.com>
Signed-off-by: Jakub Pawlak <jakub.pawlak@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>