IB/core: Move opa_class_port_info definition to header file

Both opa_vnic and the hfi driver use the same opa_classport_info
definition. We will also have ib_sa capable of querying opa class
port info and would need this definition. Move it to ib_mad.h
for everyone to use.

Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>