Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "lib.sh: AArch64: Use VGA video mode for guests"
  - lib.sh: AArch64: Use VGA video mode for guests

    On AArch64, there is no Cirrus video, so use VGA mode instead.

    On Debian systems, also fix a missing link for vgabios-stdvga.bin.
    Based on previous Armband work from [1].

    [1] https://github.com/opnfv/armband/blob/danube.2.0/patches/fuel-library/
        arm64-bug-fixes/0002-Install-vgabios-and-link-for-aarch64.patch

    Change-Id: Ia84ea5536b68e14993b719488375b0041183a767
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 530987f..f8137ae 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 530987f59295ca04b340f5dc7fd2abc53839a85f
+Subproject commit f8137ae0ea1c41c2e37a7ccd2a5d4b65a37e5dba