ethernet: tundra: Drop forward declaration of static functions

Usually it's not necessary to declare static functions if the symbols are
in the right order. Moving the definition of tsi_eth_driver down in the
compilation unit allows to drop two such declarations.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220919131515.885361-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>