cmake: set CMP0116 policy to old, Ninja DEPFILE behaviour

Fixes: #36185

CMake >=3.20 now supports relative paths in Ninja depfiles.

As Zephyr still supports the use of CMake 3.13, and the current use of
DEPFILE in linker/ld/target.cmake is already absolute path, then the
safest choice is to use old behavior.
This can be changed when Zephyr increases minimum required CMake to be
3.20 or newer.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>