.travis.yml: initial travis config for building

As I'm adding gcc-4.8 later I've add the toolchain PPA to bring in the
right build-deps.
binutils: update to the latest 2.24 release

At the same time I've switched the submodule to use the latest git
repository as the current configured one no longer works. The history
seems slightly different so the old commit-id isn't referable in this
repo.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
gcc: update to 4.8
linux: update to 3.14
new target: aarch64