Merge remote-tracking branch 'remotes/dgibson/tags/libfdt-20181002' into staging

Update dtc submodule to v1.4.7

We have some upcoming things planned for ppc that will require some
newer libfdt features.  In preparation, update the dtc/libfdt
submodule to upstreasm version v1.4.7.

# gpg: Signature made Tue 02 Oct 2018 05:23:43 BST
# gpg:                using RSA key 6C38CACA20D9B392
# gpg: Good signature from "David Gibson <[email protected]>"
# gpg:                 aka "David Gibson (Red Hat) <[email protected]>"
# gpg:                 aka "David Gibson (ozlabs.org) <[email protected]>"
# gpg:                 aka "David Gibson (kernel.org) <[email protected]>"
# Primary key fingerprint: 75F4 6586 AE61 A66C C44E  87DC 6C38 CACA 20D9 B392

* remotes/dgibson/tags/libfdt-20181002:
  Update dtc/libfdt submodule to v1.4.7

Signed-off-by: Peter Maydell <[email protected]>