doc: board: xilinx: Add documentation for ZynqMP

Add missing documentation for Xilinx ZynqMP configuration with steps how
to configure it and run it.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

doc/board/xilinx/index.rst

@@ -8,3 +8,4 @@ Xilinx
 
    xilinx
    zynq
+   zynqmp

doc/board/xilinx/zynqmp.rst

@@ -0,0 +1,115 @@
+.. SPDX-License-Identifier: GPL-2.0
+..  (C) Copyright 2020 Xilinx, Inc.
+
+ZYNQMP
+======
+
+About this
+----------
+
+This document describes the information about Xilinx Zynq UltraScale+ MPSOC
+U-Boot support. Core support is available in arch/arm/mach-zynqmp folder.
+
+ZynqMP boards
+-------------
+
+* zcu100 (ultra96 v1), zcu102, zcu104, zcu106 - Evaluation boards
+* zc1232 - Characterization boards
+* zcu111, zcu208, zcu216 - RFSOC evaluation boards
+* zcu1254, zcu1275, zcu1285 - RFSOC characterization boards
+* a2197 - System Controller on Versal boards
+* mini - Mini U-Boot running out of OCM
+* zc1751 - Characterization Processor boards
+     - zc1751-xm015-dc1
+     - zc1751-xm016-dc2
+     - zc1751-xm017-dc3
+     - zc1751-xm018-dc4
+     - zc1751-xm019-dc5
+
+Building
+--------
+
+Configure and build for zcu102 board::
+
+   $ source arm64 toolchain
+   $ export DEVICE_TREE=zynqmp-zcu102-revA
+   $ make xilinx_zynqmp_virt_defconfig
+   $ make
+
+U-Boot SPL flow
+---------------
+
+For getting U-Boot SPL flow up and running it is necessary to do some additional
+steps because booting device requires external images which are not the part of
+U-Boot repository.
+
+PMU firmware
+^^^^^^^^^^^^
+The Platform Management Unit (PMU) RAM can be loaded with a firmware (PMU
+Firmware) at run-time and can be used to extend or customize the functionality
+of PMU. The PMU firmware is the part of boot image (boot.bin) and it is
+automatically loaded by BootROM. boot.bin can be directly generated by mkimage
+tool as the part of make. If you want to create boot.bin with PMU Firmware
+include please point CONFIG_PMUFW_INIT_FILE to PMU firmware binary. For example:::
+
+  CONFIG_PMUFW_INIT_FILE="<path>/pmu.bin"
+
+If you see below message you need to load PMU Firmware::
+
+  PMUFW is not found - Please load it!
+
+The second external blob is PMU Configuration object which is object which is
+passed from U-Boot SPL to PMU Firmware for initial system configuration. PMU
+configuration object is the part of U-Boot SPL image. For pointing to this
+object please use CONFIG_ZYNQMP_SPL_PM_CFG_OBJ_FILE symbol. For example:::
+
+  CONFIG_ZYNQMP_SPL_PM_CFG_OBJ_FILE="<path>/pmu_obj.bin"
+
+
+PMU configuration object
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Object can be obtain in several ways. The easiest way is to take pm_cfg_obj.c
+from SDK/Vitis design and build it:::
+
+  $ git clone https://github.com/Xilinx/embeddedsw.git
+  $ export EMBEDDED_SW=$PWD/embeddedsw
+  $ gcc -c pm_cfg_obj.c -I ${EMBEDDED_SW}/lib/bsp/standalone/src/common/ -I ${EMBEDDED_SW}/lib/sw_services/xilpm/src/zynqmp/client/common/
+  $ objcopy -O binary pm_cfg_obj.o pmu_obj.bin
+
+The second way is to use tools/zynqmp_pm_cfg_obj_convert.py. For more
+information about this tool please run it with -h parameter.
+
+The third way is to extract it from Xilinx FSBL elf file. Object is starting at
+XPm_ConfigObject symbol.
+
+
+Arm Trusted Firmware (ATF)
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+U-Boot itself can run from EL3 to EL1. Without ATF U-Boot runs in EL3. Boot flow
+is U-Boot SPL->U-Boot in EL3. When ATF is used U-Boot normally runs in EL2. Boot
+flow is U-Boot SPL->ATF->U-Boot in EL2. As the part of build process u-boot.itb
+is generated. When BL31 shell variable is present u-boot.itb is generated with
+ATF included. You can point to it by:::
+
+  $ export BL31=<path>/bl31.bin
+
+Flashing
+--------
+
+SD Card
+^^^^^^^
+
+To write an image that boots from a SD card first create a FAT32 partition
+and a FAT32 filesystem on the SD card::
+
+        sudo fdisk /dev/sdx
+        sudo mkfs.vfat -F 32 /dev/sdx1
+
+Mount the SD card and copy the SPL and U-Boot to the root directory of the
+SD card::
+
+        sudo mount -t vfat /dev/sdx1 /mnt
+        sudo cp spl/boot.bin /mnt
+        sudo cp u-boot.itb /mnt