Currently the original datastore returned by this function doesn't
always work as the tune isn't set back to the original. Fix it
to work like all_multilib_tune_list() in utils.bbclass and correct
the data returned.
(From OE-Core rev: 4e1dc858fbf671ef27089a2b9bcdc965fe19d698)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>