Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Initial Release files from Euphrates Release"
  - Initial Release files from Euphrates Release

    These files normally contain the start point of the stable/release branch,
    but as this is the initial setup starting from the previous release,
    they contain the tip of the stable branch.

    When a project is ready to being the stable branch process, they will
    copy their project's release file and modify the 'branches' mapping to
    create their stable branch.

    Change-Id: I0244da5eeb94c431d83f217ec07b08553fdf0639
    Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>