configs: j7200_evm_a72_defconfig: Enable DP83867 Ethernet PHY

configs: j7200_evm_a72_defconfig: Enable DP83867 Ethernet PHY

The MCU Ethernet Interface on J7200-EVM uses the DP83867 Ethernet PHY as
described in the section '4.9 MCU Ethernet Interface' of the J7200-EVM
User-Guide [0]. Since the config corresponding to the DP83867 PHY has not
been enabled, the Generic PHY driver is used. As a result, the RGMII delays
do not take effect leading to packet losses.

Fix this by enabling the config for the DP83867 Ethernet PHY.

[0]: https://www.ti.com/lit/ug/spruiw7a/spruiw7a.pdf

Fixes: f8c1e893c82f ("configs: j7200_evm_a72: Add Initial support")
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>