RFR: 8166651: OrderAccess::load_acquire &etc should have const parameters

[Kim Barrett]

Looking over the changes again, I realized there was a problem with
the changes for zero. The added const qualifier to Atomic::load would
run afoul of a non-const-qualified source for os::atomic_copy64.

I've updated all three definitions of os::atomic_copy64.  Two were in
zero-specific files.  One was in os_linux_aarch64.hpp.

Unfortunately, I wasn't able to test these additional changes, as
building zero is already broken in jdk10/hs for other reasons
(JDK-8181158).

New webrev:
full: http://cr.openjdk.java.net/~kbarrett/8166651/hotspot.02/
incr: http://cr.openjdk.java.net/~kbarrett/8166651/hotspot.02.inc/