Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "[PATCH] Patch for Yardstick arm64 netperf_install.bash"
  - [PATCH] Patch for Yardstick arm64 netperf_install.bash

    Change-Id: Ic384c4603e7482f150fd4c4d2d6a6448a45ddb9e
    Signed-off-by: Trevor Tao <trevor.tao@arm.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 804a541..1bd39dc 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 804a541be394f794047a55091c9378c605e9e7ec
+Subproject commit 1bd39dc28a422c98d95451d9893c51bf3867806c