board: microsoft: surface-rt: add Microsoft Surface RT support

Surface RT is a hybrid tablet computer developed and manufactured
by Microsoft and shipped with Windows RT. The tablet uses a 1.3 GHz
quad-core Nvidia Tegra 3 chipset with 2 GB of RAM, features 10.8
inch 1366x768 screen and 32/64 GB of internal memory that can be
supplemented with a microSDXC card giving up to 200 GB of
additional storage.

Tested-by: Jethro Bull <jethrob@hotmail.com>
Signed-off-by: Jonas Schwöbel <jonasschwoebel@yahoo.de>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/doc/board/microsoft/index.rst b/doc/board/microsoft/index.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+Microsoft
+=========
+
+.. toctree::
+   :maxdepth: 2
+
+   surface-rt
diff --git a/doc/board/microsoft/surface-rt.rst b/doc/board/microsoft/surface-rt.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for the Microsoft Surface RT tablet
+==========================================
+
+Quick Start
+-----------
+
+- Build U-Boot
+- Boot
+
+Build U-Boot
+------------
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=arm-linux-gnueabi-
+    $ make surface-rt_defconfig
+    $ make
+
+After the build succeeds, you will obtain the final ``u-boot-dtb-tegra.bin``
+image, ready for loading.
+
+Boot
+----
+
+Currently, U-Boot can be preloaded into RAM via the Fusée Gelée. To enter
+RCM protocol use ``power`` and ``volume up`` key combination from powered
+off device. The host PC should recognize an APX device.
+
+Built U-Boot ``u-boot-dtb-tegra.bin`` can be loaded from fusee-tools
+directory with
+
+.. code-block:: bash
+
+    $ ./run_bootloader.sh -s T30 -t ./bct/surface-rt.bct
+
+To boot Linux, U-Boot will look for an ``extlinux.conf`` on MicroSD and then on
+eMMC. Additionally, if the Volume Down button is pressed while loading, the
+device will enter bootmenu. Bootmenu contains entries to mount MicroSD and eMMC
+as mass storage, fastboot, reboot, reboot RCM, poweroffand enter U-Boot console.