net: fjes: Reorder symbols to get rid of a few forward declarations

Quite a few of the functions and other symbols defined in this driver had
forward declarations. They can all be dropped after reordering them.

This saves a few lines of code and reduces code duplication.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220917225142.473770-1-u.kleine-koenig@pengutronix.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>