feat(versal-net): add documentation for Versal NET SoC

Add description for Versal NET SoC.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Akshay Belsare <Akshay.Belsare@amd.com>
Change-Id: Idcbb893c6b9e46512308c53ba2a0bee48a022b0a

docs/plat/index.rst

@@ -43,6 +43,7 @@ Platform Ports
    synquacer
    stm32mp1
    ti-k3
+   xilinx-versal-net
    xilinx-versal
    xilinx-zynqmp
    brcm-stingray

docs/plat/xilinx-versal-net.rst

@@ -0,0 +1,31 @@
+Xilinx Versal NET
+=================
+
+Trusted Firmware-A implements the EL3 firmware layer for Xilinx Versal NET.
+The platform only uses the runtime part of TF-A as Xilinx Versal NET already
+has a BootROM (BL1) and PMC FW (BL2).
+
+BL31 is TF-A.
+BL32 is an optional Secure Payload.
+BL33 is the non-secure world software (U-Boot, Linux etc).
+
+To build:
+```bash
+make RESET_TO_BL31=1 CROSS_COMPILE=aarch64-none-elf- PLAT=versal_net bl31
+```
+
+Xilinx Versal NET platform specific build options
+-------------------------------------------------
+
+*   `VERSAL_NET_ATF_MEM_BASE`: Specifies the base address of the bl31 binary.
+*   `VERSAL_NET_ATF_MEM_SIZE`: Specifies the size of the memory region of the bl31 binary.
+*   `VERSAL_NET_BL32_MEM_BASE`: Specifies the base address of the bl32 binary.
+*   `VERSAL_NET_BL32_MEM_SIZE`: Specifies the size of the memory region of the bl32 binary.
+
+*   `VERSAL_NET_CONSOLE`: Select the console driver. Options:
+    -   `pl011`, `pl011_0`: ARM pl011 UART 0
+    -   `pl011_1`         : ARM pl011 UART 1
+
+*   `TFA_NO_PM` : Platform Management support.
+    -    0 : Enable Platform Management (Default)
+    -    1 : Disable Platform Management