Update git submodules

* Update docs/submodules/armband from branch 'stable/danube'
  - docs: Refresh Makefile related instructions

    While at it, add instructions for selecting the custom kernel
    from Armband DEB repos.

    JIRA: ARMBAND-243

    Change-Id: Ie8828241dc3a83d7268dfbd3526303dc674aef10
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
    (cherry picked from commit 0585a2ceb59f3eacd53f2a4546d6791eb154d562)

diff --git a/docs/submodules/armband b/docs/submodules/armband
index cd4446c..dd2520e 160000 (submodule)
--- a/docs/submodules/armband
+++ b/docs/submodules/armband
@@ -1 +1 @@
-Subproject commit cd4446c0d0eff64a52ff40aa436c7a38e962b04f
+Subproject commit dd2520ebf460d27c6b4ba7c3bdebb2b7532b2f29