Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "spec: PDF and IDF support"
  - spec: PDF and IDF support

    XCI baremetal is a big feature which will require a lot of patches and lines of
    code. Before starting the contributions, a spec will allow us to discuss and
    agree on the general aspects of its architecture and implementation. That will
    hopefully facilitate and increase the velocity of its reviews.

    This patch provides a spec with the general design ideas for the infra_manager
    tool which will allow XCI to be deployed on baremetal. Its architecture is
    based on the contributions from David. All the content of the spec is questionable
    even the structure of the spec :)

    Change-Id: Ie4b096482c8150a04d3d3b2df0e2ca8a280aad10
    Signed-off-by: Manuel Buil <mbuil@suse.com>