Add bits needed to reset the frame engine on MT7988.

Fixes: 445eb644 ("net: ethernet: mtk_eth_soc: add basic support for MT7988 SoC")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/89b6c38380e7a3800c1362aa7575600717bc7543.1692721443.git.daniel@makrotopia.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>