FROMLIST: binder: refactor binder ref inc/dec for thread safety

(from https://patchwork.kernel.org/patch/9817781/

)

Once locks are added, binder_ref's will only be accessed
safely with the proc lock held. Refactor the inc/dec paths
to make them atomic with the binder_get_ref* paths and
node inc/dec. For example, instead of:

  ref = binder_get_ref(proc, handle, strong);
  ...
  binder_dec_ref(ref, strong);

we now have:

  ret = binder_dec_ref_for_handle(proc, handle, strong, &rdata);

Since the actual ref is no longer exposed to callers, a
new struct binder_ref_data is introduced which can be used
to return a copy of ref state.

Change-Id: I11e6a31963eb18f5788cd52ae6ec9adb4438fa48
Signed-off-by: Todd Kjos <tkjos@google.com>