IB/core: Add macros for declaring methods and attributes

This patch adds macros for declaring objects, methods and
attributes. These definitions are later used by downstream patches
to declare some of the default types.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>