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
    
1 file changed