xtensa: ISS: don't allocate memory in platform_setup

commit ef439d49e0bfb26cd5f03c88b4cb7cc9073ed30c upstream.

Memory allocator is not initialized at that point yet, use static array
instead.

Cc: stable@vger.kernel.org
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>