configs: am65x_evm_defconfig: Enable I2C support

Enable I2C via driver model as well as the associated set of U-Boot
commands to allow us interacting with various I2C slave devices.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>