configs: am64x_evm_a53_defconfig: Enable DP83867 PHY driver

AM64x GP and SK EVM have DP83867 PHY connected to CPSW external port0.
Enable the driver in order to use ethernet at U-Boot prompt.
CONFIG_PHY_TI is selected by CONFIG_PHY_TI_DP83867 and thus can be dropped.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>