Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - docs: Add XCI overview document

    Change-Id: I23405aec19a7e9bfce1c58d770b80b1c9c550d00
    Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>

diff --git a/docs/submodules/releng-xci b/docs/submodules/releng-xci
index a906168..52fea9e 160000 (submodule)
--- a/docs/submodules/releng-xci
+++ b/docs/submodules/releng-xci
@@ -1 +1 @@
-Subproject commit a90616876a71042422c26833186cacbce85102a4
+Subproject commit 52fea9ecfc8cf0e81185b3f53f3d9d4d2ab98c9c