xtensa: Export __invalidate_icache_range

When modular code calls flush_icache_range():

    ERROR: "__invalidate_icache_range" [drivers/misc/lkdtm.ko] undefined!
    make[1]: *** [__modpost] Error 1

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/xtensa_ksyms.c

@@ -105,6 +105,7 @@ EXPORT_SYMBOL(csum_partial_copy_generic);
  * Architecture-specific symbols
  */
 EXPORT_SYMBOL(__xtensa_copy_user);
+EXPORT_SYMBOL(__invalidate_icache_range);
 
 /*
  * Kernel hacking ...