atf: new package

ATF, or Automated Testing Framework, is a collection of libraries to
write test programs in C, C++ and POSIX shell.

https://github.com/jmmv/atf



Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>