bfd: rename parsing methods of object attribute v1 API

bfd: rename parsing methods of object attribute v1 API

This patch is a preparation for the introduction of object attributes
v2. It aims at:
- making clear what methods are used to parse OAv1
- adding more constaints on parameters type by using enums instead of
defines.
- hiding the attribute tag type behind a typedef.
- preparing the move of object attributes's parsing code to another
  file.

Note: the name obj_attr_v1_process_attribute is exposed in the API.
Ideally, the version should not be part of the name, and be hidden
behind a macro. However, a later patch will unify the parsing of
OAv1 and OAv2, and will make the use of such a macro obsolete.