x86, kaslr: Clarify RANDOMIZE_BASE_MAX_OFFSET

The help text for RANDOMIZE_BASE_MAX_OFFSET was confusing. This has been
clarified, and updated to be an export-only tunable.

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/20131210202745.GA2961@www.outflux.net


Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>