Update git submodules

* Update docs/submodules/qtip from branch 'stable/euphrates'
  - Add missing link for euphrates release notes

    Change-Id: Icc0067e961c497f203996eafedec3e316ea6e5ff
    Signed-off-by: Yujun Zhang <zhang.yujunz@zte.com.cn>
    (cherry picked from commit 4daf79855c2dccff22134939245497140343bfa3)

  - Use frozen requirements

    Change-Id: I3de2e7d3fc2e88d0556b35c34830d7eab522d404
    Signed-off-by: Yujun Zhang <zhang.yujunz@zte.com.cn>

diff --git a/docs/submodules/qtip b/docs/submodules/qtip
index af983e4..0a90de8 160000 (submodule)
--- a/docs/submodules/qtip
+++ b/docs/submodules/qtip
@@ -1 +1 @@
-Subproject commit af983e483333615d6528df2489975c866c3f3e54
+Subproject commit 0a90de857e868b06a673e4980e313e34e9170b2b