cmake: support ELF image adjustment

This commit adds support for adjust the addresses of the final image.
This is useful when the image is to be flashed at a location different
from the LMA address encoded in the ELF file by the linker.

An example use-case is multicore systems where core A might load image
from a flash partition into RAM in order for core B to execute and load,
but where the image itself is build with the RAM addresses as LMA.

It updates the zephyr_image_info.h header with information of adjustment
value.

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