stress: add new package

Deliberately simple workload generator for POSIX systems. It imposes
a configurable amount of CPU, memory, I/O, and disk stress on the system.

Moving the package from meta-linaro as a dependency for rt-tests ptest

Signed-off-by: Maxin B. John <maxin.john@enea.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>