boards: mps2_an521: build non-secure Zephyr images together with TF-M

By default, if we build for a Non-Secure version of the board,
force building with TF-M as the Secure Execution Environment.
An exception is when we build openamp samples, where the non-
secure image is basically used for the remote core.

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