device: add post-process of elf file to manage device handles

Following the idiom used for system calls, add script support to read
the initial application binary to identify which devices are defined,
and to use their offset in the device array as their unique handle
rather than the externally-defined ordinal from devicetree.  The
device dependency arrays are updated to use these handles.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>