media: docs: move uAPI book to userspace-api/media

Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee38 ("docs: Create a user-space API guide").

As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.

Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/v4l/v4l2-selection-flags.rst

@@ -0,0 +1,51 @@
+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _v4l2-selection-flags:
+
+***************
+Selection flags
+***************
+
+.. tabularcolumns:: |p{5.2cm}|p{2.0cm}|p{6.5cm}|p{1.2cm}|p{1.6cm}|
+
+.. _v4l2-selection-flags-table:
+
+.. flat-table:: Selection flag definitions
+    :header-rows:  1
+    :stub-columns: 0
+
+    * - Flag name
+      - id
+      - Definition
+      - Valid for V4L2
+      - Valid for V4L2 subdev
+    * - ``V4L2_SEL_FLAG_GE``
+      - (1 << 0)
+      - Suggest the driver it should choose greater or equal rectangle (in
+	size) than was requested. Albeit the driver may choose a lesser
+	size, it will only do so due to hardware limitations. Without this
+	flag (and ``V4L2_SEL_FLAG_LE``) the behaviour is to choose the
+	closest possible rectangle.
+      - Yes
+      - Yes
+    * - ``V4L2_SEL_FLAG_LE``
+      - (1 << 1)
+      - Suggest the driver it should choose lesser or equal rectangle (in
+	size) than was requested. Albeit the driver may choose a greater
+	size, it will only do so due to hardware limitations.
+      - Yes
+      - Yes
+    * - ``V4L2_SEL_FLAG_KEEP_CONFIG``
+      - (1 << 2)
+      - The configuration must not be propagated to any further processing
+	steps. If this flag is not given, the configuration is propagated
+	inside the subdevice to all further processing steps.
+      - No
+      - Yes