Build: Export recommended tf-m-tests version

Parse recommended tf-m-tests version from version.txt and export it to
NS build.
tf-m-tests can read this version to check compatiablity.

Change-Id: Ibd3d6dab3d53a774d0f14aaa9dc2f97e467dc728
Signed-off-by: David Hu <david.hu@arm.com>
4 files changed