objtool, kcsan: Add volatile read/write instrumentation to whitelist

Adds KCSAN's volatile instrumentation to objtool's uaccess whitelist.

Recent kernel change have shown that this was missing from the uaccess
whitelist (since the first upstreamed version of KCSAN):

  mm/gup.o: warning: objtool: fault_in_readable+0x101: call to __tsan_volatile_write1() with UACCESS enabled

Fixes: 75d75b7a ("kcsan: Support distinguishing volatile accesses")
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>