arm64: dts: ti: am654: Add DSS node

Add DSS node to k3-am65-main.dtsi with labels for board specific
support and syscon node for oldi-io-ctrl.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>