.travis.yml: Add description to each job

.travis.yml: Add description to each job

The NAME variable can be used to describe nicely a job (see [*]).
As we currently have 32 jobs, use it. This helps for quickly
finding a particular job.

  before: https://travis-ci.org/qemu/qemu/builds/639887646
  after: https://travis-ci.org/philmd/qemu/builds/641795043

[*] https://docs.travis-ci.com/user/customizing-the-build/#naming-jobs-within-matrices

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200125183135.28317-1-f4bug@amsat.org>
Message-Id: <20200203090932.19147-9-alex.bennee@linaro.org>