arc: cleanup linker scripts to include autoconf.h first

The various linker scripts on arc would include autoconf.h in the arch
linker script but might have CONFIG_ symbols referenced in the soc
specific linker script.  Move autoconf.h inclusion to top of the soc
specific linker script out of the arch specific one so we know
autoconf.h is seen before any CONFIG_ references.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>