stmmac: remove setup/free glue callbacks

As all dwmac-* drivers have been converted to have a proper probe
function the setup callback can now be removed. Also remove the
free callback that wasn't used by any driver.

New dwmac-* drivers should implement standard probe and remove
functions to preform any needed setup and teardown.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>