Build: Decouple NS from config_impl.cmake

config_impl.cmake collects some SPM specific config flags. Those config
flags are transparent to NS developers.
Remove NS dependency on those config flags to simplify NS integration
with TF-M.

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: I39f53284dbf34a42e0ea745fdcd73f493807988d
1 file changed