armclang: armlinker: armlink symbol steering file

This commit introduces armlink steering file.

A steering file in armlink allows Zephyr to keep using existing linker
symbols defined in ld scripts and used throughout the code tree.

The steering file is generated at build time in order to resolve Zephyr
linker symbols to their corresponding armlink symbols.

As example, Zephyr defines __ramfunc_start which corresponds to the
armlink auto defined Image$$ramfunc$$Base symbol.

Or __init_PRE_KERNEL_1_start which corresponds to Image$$init_0$$Base.

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