arm64: dts: ti: k3-j784s4-main: Add system controller and SERDES lane mux

The system controller node manages the CTRL_MMR0 region.
Add serdes_ln_ctrl node which is used for controlling the SERDES lane mux.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
[j-choudhary@ti.com: Fix serdes_ln_ctrl node]
Signed-off-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Link: https://lore.kernel.org/r/20231019054022.175163-2-j-choudhary@ti.com


Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>