doc: android: Convert to Sphinx format

Convert Android documentation from regular txt format to Sphinx (RST).
Also add Android index.rst file and reference it in root index.rst, so
that Android documentation is visible.

Test:

    $ make htmldocs
    $ xdg-open doc/output/index.html

Signed-off-by: Sam Protsenko <joe.skb7@gmail.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/doc/android/ab.rst b/doc/android/ab.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+Android A/B updates
+===================
+
+Overview
+--------
+
+A/B system updates ensures modern approach for system update. This feature
+allows one to use two sets (or more) of partitions referred to as slots
+(normally slot A and slot B). The system runs from the current slot while the
+partitions in the unused slot can be updated [1]_.
+
+A/B enablement
+--------------
+
+The A/B updates support can be activated by specifying next options in
+your board configuration file::
+
+    CONFIG_ANDROID_AB=y
+    CONFIG_CMD_AB_SELECT=y
+
+The disk space on target device must be partitioned in a way so that each
+partition which needs to be updated has two or more instances. The name of
+each instance must be formed by adding suffixes: ``_a``, ``_b``, ``_c``, etc.
+For example: ``boot_a``, ``boot_b``, ``system_a``, ``system_b``, ``vendor_a``,
+``vendor_b``.
+
+As a result you can use ``ab_select`` command to ensure A/B boot process in your
+boot script. This command analyzes and processes A/B metadata stored on a
+special partition (e.g. ``misc``) and determines which slot should be used for
+booting up.
+
+Command usage
+-------------
+
+.. code-block:: none
+
+    ab_select <slot_var_name> <interface> <dev[:part_number|#part_name]>
+
+for example::
+
+    => ab_select slot_name mmc 1:4
+
+or::
+
+    => ab_select slot_name mmc 1#misc
+
+Result::
+
+    => printenv slot_name
+    slot_name=a
+
+Based on this slot information, the current boot partition should be defined,
+and next kernel command line parameters should be generated:
+
+* ``androidboot.slot_suffix=``
+* ``root=``
+
+For example::
+
+    androidboot.slot_suffix=_a root=/dev/mmcblk1p12
+
+A/B metadata is organized according to AOSP reference [2]_. On the first system
+start with A/B enabled, when ``misc`` partition doesn't contain required data,
+the default A/B metadata will be created and written to ``misc`` partition.
+
+References
+----------
+
+.. [1] https://source.android.com/devices/tech/ota/ab
+.. [2] https://android.googlesource.com/platform/bootable/recovery/+/refs/tags/android-10.0.0_r25/bootloader_message/include/bootloader_message/bootloader_message.h