configs: ls1021a-tsn: enable sja1105 switch driver

The sja1105 is a 5-port switch that uses a DM_DSA driver. Its 5th (CPU)
port is connected internally to the eth2 port of the LS1021A SoC.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>