Update git submodules

* Update docs/submodules/armband from branch 'master'
  - MaaS: preseed Armband repo via curtin

    Instead of installing upstream vanilla kernel from Ubuntu just to
    upgrade to the one from Armband repo later, preseed Armband repo
    config via curtin.
    This allows us to drop a kernel update cycle, thus saving a few
    minutes at each deploy.

    While at it, switch salt repo addition to use the maas region reclass
    section instead of adding a dedicated mechanism for it in the curtin
    template (only for arm64).

    JIRA: ARMBAND-280

    Change-Id: Iad5953a7de80d728f11a4ce3113bd7725100c31c
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/armband b/docs/submodules/armband
index 99c1030..648ec98 160000 (submodule)
--- a/docs/submodules/armband
+++ b/docs/submodules/armband
@@ -1 +1 @@
-Subproject commit 99c10303e7f2c02010677f97512f161cd3a8abf7
+Subproject commit 648ec98613d31e3d9701b9ac1d87aed640b245f3