lkdtm: flush icache and report actions

Some CPUs explicitly need to have their icache flushed after making
executable code copies for the memory region execution tests.
Additionally, report the specific address targets being used so that
debugging non-crash failures is easier.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>