arm64: dts: ls1088a: add internal PCS for DPMAC1 node

A previous patch added the PCS for DPMAC2 only, as
used for the AQR PHY on the LS1088ARDB.

DPMAC1 PCS access is required for PHYLINK SFP support
on the Traverse Ten64 board.

Signed-off-by: Mathew McBride <matt@traverse.com.au>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>