arm64: dts: ti: iot2050: Factor out DP related bits

There is a variant coming which does not support the Display Port. Move
all related bits into a separate dtsi so that only those variants
supporting the interface can include it.

Along that, remove a redundant clock setting from
k3-am65-iot2050-common-pg1.dtsi.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Link: https://lore.kernel.org/r/3397d917d7c97f7aec05bc5f65eef3a6fe843650.1707463401.git.jan.kiszka@siemens.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>