.travis.yml: Add Coverity addon
.travis.yml: Add Coverity addon

Enables Travis to perform a Coverity build and scan when a push
is made to the coverity_scan branch. In this case, the regular
build script is not necessary and skipped to save time.

The Coverity build is currently based on the default qemu
configuration.

Signed-off-by: Victor Chong <4aabb03bd6dd29c44a49684d87b08ac07e10b492@linaro.org>
Reviewed-by: Joakim Bech <741f90e2a7f4d9afbad8bd50be20560f4cf38962@linaro.org>
Reviewed-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os