boards: mps2_an521: add empty CPU0 binary for AN521

Add a project to build an empty binary for AN521 CPU0,
which will only serve to wake up CPU1, and let samples,
and tests to execute as standalone applications in CPU1.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
2 files changed