travis-ci: Try harder to build all ARM targets

The way that we have things broken down currently allows for some
combinations of vendor or CPU to not be built.  To fix this, create a
new catch-all job that excludes everything we've built elsewhere.  For
the sake of simplicity we are allowing for the possibility of some
overlap between the vendor-based jobs and the CPU-based jobs.  While
we're in here, make a failed build provide the summary of failure.

Signed-off-by: Tom Rini <trini@konsulko.com>