examples: Add TF-M support

Add TF-M support and enable it by default, as Total Solutions examples
aim to demonstrate all supported features.

TF-M has a predefined memory layout for each supported platform, so add
non-secure linker scripts for supported examples, platforms and
toolchains to match TF-M's requirements.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>