arm64: dts: ti: k3-j721e-sk: Enable DisplayPort

Add the endpoint nodes to describe connection from
DSS => MHDP => DisplayPort connector.

Signed-off-by: Rahul T R <r-ravikumar@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Link: https://lore.kernel.org/r/20220505090709.9252-2-r-ravikumar@ti.com