Current build system assumes same CPU arch on secure and non secure side.
This task is to cleanly isolate secure side build from non secure side build.
a. separation of cmake files - top level configuration files are currently common across secure and non secure build. The configurations must be separated out between secure and non secure builds. Proposed tree:
tf-m/ConfigXXX.cmake -- only configure the bootloader and secure side build.
tf-m/app/ConfigXXX.cmake --- config files for non-secure file build