tools/imagetool: remove linker script

Commit a93648d1 introduced linker generated
lists for imagetool which is the base for some host tools (mkimage, dumpimage,
et al.).  Unfortunately some host tool chains do not support the used type of
linker scripts. Therefore this commit broke these host-tools for them, namely
FreeBSD and Darwin (OS/X).

This commit tries to fix this. In order to have a clean distinction between host
and embedded code space we need to introduce our own linker generated list
instead of re-using the available linker_lists.h provided functionality.  So we
copy the implementation used in linux kernel script/mod/file2alias.c which has
the very same problem (cause it is a host tool). This code also comes with an
abstraction for Mach-O binary format used in Darwin systems.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
Cc: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>