ci: Include all configurations in Coverity scan

ci: Include all configurations in Coverity scan

Coverity only provides us as OSS project a single "stream", thus a
single configuration for our project. But we already have 3. However,
we can accumulate results to a certain degree with some tricks: We have
to ensure that the intermediate "make clean" runs are not tracked by
cov-build, the build tracker of Coverity.

That's why we overload the default scan-build script of Travis CI and
Coverity, obtain the original one from our script, patch that version
to run our build script in a way that we have control over what gets
tracked and what not. Nasty, but seems to work sufficiently for now.

In addition, we need to register the ARM cross-compiler via
cov-configure.

At this chance: "description" is no longer used by Coverity - drop it.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>