arm: dts: ls1028a: add an empty /soc

arm: dts: ls1028a: add an empty /soc

To keep the device tree similar to the linux kernel one, we need to move
all CCSR related devices into the /soc node. To keep the patches easy to
review, we initially add an empty /soc node and populate it piece by
piece.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>