arm64: dts: ls1028a: add missing CAN nodes

The LS1028A has two FlexCAN controller. These are compatible with
the ones from the LX2160A. Add the nodes.

The first controller was tested on the Kontron sl28 board.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>