Update dtc to include build fix

Build fix:
    libfdt: Correct condition for reordering blocks

This change also include one extra commit that seems to be a unit test
only.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

diff --git a/dtc b/dtc
index 85e5d839847af54efab170f2b1331b2a6421e647..b6910bec11614980a21e46fbccc35934b671bd81 160000 (submodule)
--- a/dtc
+++ b/dtc
@@ -1 +1 @@
-Subproject commit 85e5d839847af54efab170f2b1331b2a6421e647
+Subproject commit b6910bec11614980a21e46fbccc35934b671bd81