travis: qemu_v8: fetch dtc submodule to avoid issues with libfdt-dev

If the libfdt-packe is missing or is too old, QEMU reports the
following error:

ERROR: DTC (libfdt) version >= 1.4.2 not present. Your options:
         (1) Preferred: Install the DTC (libfdt) devel package
         (2) Fetch the DTC submodule, using:
             git submodule update --init dtc

It looks like the version of libfdt-dev that is currently deployed on
travis-ci.org is too old. So, let's do (2).

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Reviewed-by: Igor Opaniuk <igor.opaniuk@linaro.org>

.travis.yml

@@ -58,5 +58,7 @@ script:
   # in the makefile
   - if [ $REPO_PROJ == "fvp" ]; then mkdir -p $HOME/$REPO_PROJ/Foundation_Platformpkg; fi
   - cd $HOME/$REPO_PROJ && repo init -u https://github.com/OP-TEE/manifest.git -m $REPO_PROJ.xml </dev/null && repo sync -j2 --no-clone-bundle --no-tags --quiet
+  # Fetch a local copy of dtc+libfdt to avoid issues with a possibly outdated libfdt-dev
+  - if [ $REPO_PROJ == "qemu_v8" ]; then cd $HOME/$REPO_PROJ/qemu && git submodule update --init dtc; fi
   - cd $HOME/$REPO_PROJ && ln -s $HOME/reference/toolchains .
   - cd $HOME/$REPO_PROJ/build && make all -j2