uboot-mediatek: fix BT-R320 Ethernet mode
The CPU port between the MT7981 and MT7531 runs at 2.5 Gbps, but the U-Boot
device tree configures it as SGMII at 1 Gbps. This leaves Ethernet unable
to exchange packets despite an active physical link.
Use 2500base-x and a 2500 Mbps fixed link, matching the Linux device tree.
Fixes: a3105d3f9573 ("mediatek: filogic: add support for Globitel BT-R320")
Signed-off-by: Bogdan K <zikwarface134@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24372
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>