dtc: Update dtc / libfdt submodule to version 1.4.0

Since some recent patches require libfdt version 1.4.0,
let's update the dtc submodule to this version.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NAlexander Graf <agraf@suse.de>

dtc @ 65cc4d27

-Subproject commit bc895d6d09695d05ceb8b52486ffe861d6cfbdde
+Subproject commit 65cc4d2748a2c2e6f27f1cf39e07a5dbabd80ebf