net: mtk_eth_soc: move MAC_MCR setting to mac_finish()

Move the setting of the MTK_MAC_MCR register from the end of mac_config
into the phylink mac_finish() method, to keep it as the very last write
that is done during configuration.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>