arm64: dts: ti: k3-j721e-common-proc-board: add DP to j7 evm

Add the endpoint nodes to describe connection from
DSS => MHDP => DisplayPort connector.
Also add the required pinmux nodes for hotplug.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
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/20220429112639.13004-3-r-ravikumar@ti.com