Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Update kvm4nfv commit id

    This kvm4nfv commit includes changes for the config file which disable
    vt-d by default and has the x2apic enabled.

    Change-Id: I2e8085792fb8222dfc59d4ece0ac58ec9a16c1bd
    Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index d3e6779..78c835c 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit d3e677982d7293de86f22b1770ae15a3609bf89c
+Subproject commit 78c835c56466726e8c5a99942d5179714907b5f4