travis: reduce coverage of gprof build
This build is regularly timing out and even switching off linux-user
wasn't enough. Instead explicitly choose a target list of broadly the
"major" architectures. This is enough to check the gprof build
machinery works without worrying about the actual coverage results.
I did try various YAML constructs for specifying CONFIG with
continuation but couldn't get any of them to work hence the very long
line.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>