arm64: dts: ti: Add initial support for AM68 SK System on Module

AM68 Starter Kit (SK) is a low cost, small form factor board designed
for TI’s AM68 SoC. TI’s AM68 SoC comprises of dual core A72, high
performance vision accelerators, hardware accelerators, latest C71x
DSP, high bandwidth real-time IPs for capture and display. The SoC is
power optimized to provide best in class performance for industrial
applications.

    AM68 SK supports the following interfaces:
      * 16 GB LPDDR4 RAM
      * x1 Gigabit Ethernet interface
      * x1 USB 3.1 Type-C port
      * x2 USB 3.1 Type-A ports
      * x1 PCIe M.2 M Key
      * 512 Mbit OSPI flash
      * x2 CSI2 Camera interface (RPi and TI Camera connector)
      * 40-pin Raspberry Pi GPIO header

SK's System on Module (SoM) contains the SoC and DDR.
Therefore, add DT node for the SOC and DDR on the SoM.

Schematics: https://www.ti.com/lit/zip/SPRR463
TRM: http://www.ti.com/lit/pdf/spruj28Signed-off-by: Sinthu Raja <sinthu.raja@ti.com>
Tested-by: Vaishnav Achath <vaishnav.a@ti.com>
Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20230116071446.28867-3-sinthu.raja@ti.com

arch/arm64/boot/dts/ti/k3-am68-sk-som.dtsi

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023 Texas Instruments Incorporated - https://www.ti.com/
+ */
+
+/dts-v1/;
+
+#include "k3-j721s2.dtsi"
+#include <dt-bindings/gpio/gpio.h>
+
+/ {
+	memory@80000000 {
+		device_type = "memory";
+		/* 16 GB RAM */
+		reg = <0x00 0x80000000 0x00 0x80000000>,
+		      <0x08 0x80000000 0x03 0x80000000>;
+	};
+
+	reserved_memory: reserved-memory {
+		#address-cells = <2>;
+		#size-cells = <2>;
+		ranges;
+
+		secure_ddr: optee@9e800000 {
+			reg = <0x00 0x9e800000 0x00 0x01800000>;
+			no-map;
+		};
+	};
+};