gcc-target: Create a LTO plugin symlink in bfd-plugins directory

This directory is scanned by binutils provided ar,ranlib,nm for plugins
that it can load automatically, putting liblto_plugin.so in their means
we do not need gcc-ar, gcc-nm, gcc-ranlib particularly as normal
ar/ranlib/nm tools will work equally well as they can now use this
linker plugin by default

This also mean we can revert back to using ar/ranlib/nm as default
providers for AR/NM/RANLIB on target

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>