boards: mps4: Enable non-secure variant support

Zephyr's TF-M has been aligned with upstream TF-M v2.2.0, which adds
support for Corstone-320 (CS320). The previous commit also updates TF-M
to fix compiler warnings seen with MPS4. So, with this update, enable
build and execution of non-secure variants of MPS4-based boards.

Signed-off-by: Sudan Landge <sudan.landge@arm.com>
4 files changed