modules: tfm: Exclude non-secure TF-M application from build

Exclude the non-secure TF-M application from being built by TF-M.
This also stops the building of the tfm_ns_api library that we were
linking against.
This library is defined by the tf-m regression tests.
Add the installed interface source files exported by the TF-M build
system compile them in the zephyr build system.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>