[SPARC64]: Improve VIO device naming further.

The best scheme to get uniqueness seems to be:

FOO			-- If node lacks "id" property
FOO-$(ID)		-- If node has "id" but parent lacks "cfg-handle"
FOO-$(ID)-$(CFG_HANDLE) -- If node has both

Signed-off-by: David S. Miller <davem@davemloft.net>