tests/plugin: add sample plugins

Pass arguments with -plugin=libfoo.so,arg=bar,arg=baz

Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
6 files changed