Support for NXP's i.MX8QX SoC

NXP's i.MX8QX is an ARMv8 SoC with 4 Cortex-A35 cores and
system controller (Cortex-M4) inside, documentation can
be found in below link:

https://www.nxp.com/products/processors-and-microcontrollers/
applications-processors/i.mx-applications-processors/i.mx-8-processors:IMX8-SERIES

This patch adds support for booting up SMP linux kernel (v4.9).

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
diff --git a/docs/plat/imx8.rst b/docs/plat/imx8.rst
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+Description
+===========
+
+The i.MX 8 series of applications processors is a feature- and
+performance-scalable multi-core platform that includes single-,
+dual-, and quad-core families based on the Arm® Cortex®
+architecture—including combined Cortex-A72 + Cortex-A53,
+Cortex-A35, and Cortex-M4 based solutions for advanced graphics,
+imaging, machine vision, audio, voice, video, and safety-critical
+applications.
+
+The i.MX8QX is with 4 Cortex-A35 ARM core and 1 Cortex-M4 system
+controller.
+
+The System Controller (SC) represents the evolution of centralized
+control for system-level resources on i.MX8. The heart of the system
+controller is a Cortex-M4 that executes system controller firmware.
+
+Boot Sequence
+=============
+
+Bootrom --> BL31 --> BL33(u-boot) --> Linux kernel
+
+How to build
+============
+
+Build Procedure
+---------------
+
+-  Prepare AARCH64 toolchain.
+
+-  Build System Controller Firmware and u-boot firstly, and get binary images: scfw_tcm.bin and u-boot.bin
+
+-  Build TF-A
+
+   Build bl31:
+
+   .. code:: shell
+
+       CROSS_COMPILE=aarch64-linux-gnu- make PLAT=<Target_SoC> bl31
+
+   Target_SoC should be "imx8qx" for i.MX8QX SoC.
+
+Deploy TF-A Images
+-----------------
+
+TF-A binary(bl31.bin), scfw_tcm.bin and u-boot.bin are combined together
+to generate a binary file called flash.bin, the imx-mkimage tool is used
+to generate flash.bin, and flash.bin needs to be flashed into SD card
+with certain offset for BOOT ROM. The system controller firmware,
+u-boot and imx-mkimage will be upstreamed soon, this doc will be updated
+once they are ready, and the link will be posted.
+
+.. _i.MX8: https://www.nxp.com/products/processors-and-microcontrollers/applications-processors/i.mx-applications-processors/i.mx-8-processors/i.mx-8-family-arm-cortex-a53-cortex-a72-virtualization-vision-3d-graphics-4k-video:i.MX8