travis: ensure official tags are available

* Clones optee_os git with a very large depth
* Fetches tags from official OP-TEE repository to make sure tags needed to
  build are in place.

Reviewed-by: Pascal Brand <pascal.brand@linaro.org>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/.travis.yml b/.travis.yml
index f0ba1fb..f9fdaf0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,6 +12,9 @@
   directories:
     - $HOME/downloads
 
+git:
+  depth: 1000000
+
 before_install:
   # Install the cross compilers
   - wget http://releases.linaro.org/15.02/components/toolchain/binaries/arm-linux-gnueabihf/gcc-linaro-4.9-2015.02-3-x86_64_arm-linux-gnueabihf.tar.xz
@@ -70,6 +73,7 @@
   - (cd $HOME/optee_repo/qemu && git submodule update --init dtc)
   - (cd $HOME/optee_repo && mv optee_os optee_os_old && ln -s $MYHOME optee_os)
   - cd $MYHOME
+  - git fetch https://github.com/OP-TEE/optee_os --tags
   - unset CC
 
 # Several compilation options are checked