Update git submodules

* Update external/dtc from branch 'master'
  to 83534bb2d821edc66db3e8324641aab26a7caaf5
  - Enable shared library for libfdt
    
    The dtc, fdtget and now crosvm.experimental host binaries can use
    libfdt. Make it a shared library instead of linking it statically into
    all of these tools.
    
    Change-Id: Ifefaaf3397ee6a1cd579bc140d03e69846e67745
    
diff --git a/external/dtc b/external/dtc
index b734cfd..83534bb 160000
--- a/external/dtc
+++ b/external/dtc
@@ -1 +1 @@
-Subproject commit b734cfd607de2050b9c477d2ede4941bd549e51d
+Subproject commit 83534bb2d821edc66db3e8324641aab26a7caaf5