toolkit: Update the comment.
toolkit: Fix the map formatting.
linkers: Add kernel symbol support.

The rtems-sym tool has been changed from a basic map tool to now
provide an object file in the specific architecture containing
the symbols in the RTEMS kernel. It can still generate a map.

The object can be embedded or loaded. It cannot be both.
linkers: Add base image symbol to ELF object file generation.

This change adds support to the rtems-syms code to generate a suitable
ELF object you can link to the base image kernel in the embed mode or
you can load with the run-time load mode.

The change fixes a bug in the framework where local ELF symbols
were being placed in the external symbol table. The external
symbol table has been removed and a global, weak and local set
of tables is now provided as this is more aligned with the ELF
format.