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 <david@gibson.dropbear.id.au>"
# gpg:                 aka "David Gibson (Red Hat) <dgibson@redhat.com>"
# gpg:                 aka "David Gibson (ozlabs.org) <dgibson@ozlabs.org>"
# gpg:                 aka "David Gibson (kernel.org) <dwg@kernel.org>"
# 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: NPeter Maydell <peter.maydell@linaro.org>

dtc @ 88f18909

-Subproject commit e54388015af1fb4bf04d0bca99caba1074d9cc42
+Subproject commit 88f18909db731a627456f26d779445f84e449536