net: ethernet: mtk_eth_soc: fix kernel-doc comment

Fix and add some missing field descriptions to kernel-doc comment of
struct mtk_eth.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/748e7de848e45ecdc84fbb78e34e9e13b9aa4329.1751461762.git.daniel@makrotopia.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>