board: motorola: add Atrix 4G MB860 and Droid X2 MB870 support

The Motorola Atrix 4G (MB860) and Droid X2 (MB870) both featured a
dual-core NVIDIA Tegra 2 AP20H processor clocked at 1GHz, coupled with 1GB
of DDR2 RAM. Storage consisted of 16GB of internal flash memory, expandable
via microSD. The display was a 4.0-inch TFT LCD with a resolution of
960x540 pixels (qHD). The devices originally ran on Android up to 2.3
(Gingerbread).

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
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+.. SPDX-License-Identifier: GPL-2.0+
+
+Motorola
+========
+
+.. toctree::
+   :maxdepth: 2
+
+   mot