IB/core: Save the device attributes on the device structure

This way both the IB core and upper level drivers can access these cached
device attributes rather than querying or caching them on their own.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>