Use addReqProv() for adding package self-provides too

Use addReqProv() for adding package self-provides too

- We have a function for this stuff so use it. This also ensures
  the per-package rpmds'es and the data in header stay in sync
  and that manually added self-provides wont cause duplicates.
(cherry picked from commit e4b7d44eac71dc4c26b5254f357d8ad786592c8c)