net: fec: Move fec_enet_eee_mode_set() and helper earlier

FEC is about to get its EEE code re-written. To allow this, move
fec_enet_eee_mode_set() before fec_enet_adjust_link() which will
need to call it.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Wei Fang <wei.fang@nxp.com>
Link: https://lore.kernel.org/r/20240302195306.3207716-7-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>