tfm_ns_interface.c is intended to be overriden by clients to support
different targets. We copy this file from upstream into the mbed-os
platform library. We also have a specific "strong" overridden version
for the NU_M2354 target, which is located in its target library.
Previously the implementations in the platform library were decorated
with __attribute__(weak), and we provided a strong definition for the
NU_M2354 target. This worked fine because of weak linking, the linker
will pick the first "strong" definition and use that, avoiding any ODR
violations. However, upstream have removed __attribute__(weak) from the
function definitions, which caused multiply defined symbol errors when
trying to build the NU_M2354 target.

To work around the above issue, we remove the common definition in the
platform library; instead we copy the file to the Musca B1 and Musca S1
target libaries. This means the appropriate tfm_ns_interface.c is only
included in the build when compiling for the specific target which uses
it.

As we still use target labels, TFM is not visible to CMake. Protect include of their scripts with the same mechanism.

- list files included via module path
- <project-name>_SOURCE_DIR for sources that are out of the current processed CMake
- CMAKE_CURRENT_LIST_DIR for listfiles

In targets.json, ARM_MUSCA_B1 and ARM_MUSCA_S1 have alias target
names suffixed with `_NS`. They are identical to targets without
`_NS` and exist purely for compatibility with the old naming
convention we had. The CI builds them as separate targets and uses
extra resources.

As we are upgrading Musca targets to TF-M v1.2, it's time to clean
up the aliases.

Files containing signing layouts are parsed by the post build
hook for signing purpose only.

Add the missing CMake targets for NS Mbed boards.

Create CMake target per each Mbed OS target.

Add CMakeLists.txt file for the target