selftests: add seccomp suite

This imports the existing seccomp test suite into the kernel's selftests
tree. It contains extensive testing of seccomp features and corner cases.
There remain additional tests to move into the kernel tree, but they have
not yet been ported to all the architectures seccomp supports:
https://github.com/redpig/seccomp/tree/master/tests



Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>