For PowerPC, GCC 5.2 is the requirement for GCC plugins.  Move the
version check to Kconfig so that the GCC plugin menus will be hidden
if an older compiler is in use.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: NAndrew Donnellan <andrew.donnellan@au1.ibm.com>
Reviewed-by: NKees Cook <keescook@chromium.org>