device: export CMake pre-load from device subsystem enumeration script

Extend the device subsystem enumeration script to produce a CMake
pre-load script.

This allow CMake linker generator scripts to create iterable sections
based on output from device subsystem enumeration.

This ensures that same functionality is available in both ld linker
templates and the linker generator.

Update linker generators to support the use of the device subsystem
enumeration CMake pre-load script.

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