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/rc/lirc-get-send-mode.rst

@@ -0,0 +1,78 @@
+.. 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
+
+.. _lirc_get_send_mode:
+.. _lirc_set_send_mode:
+
+************************************************
+ioctls LIRC_GET_SEND_MODE and LIRC_SET_SEND_MODE
+************************************************
+
+Name
+====
+
+LIRC_GET_SEND_MODE/LIRC_SET_SEND_MODE - Get/set current transmit mode.
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, LIRC_GET_SEND_MODE, __u32 *mode )
+    :name: LIRC_GET_SEND_MODE
+
+.. c:function:: int ioctl( int fd, LIRC_SET_SEND_MODE, __u32 *mode )
+    :name: LIRC_SET_SEND_MODE
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by open().
+
+``mode``
+    The mode used for transmitting.
+
+
+Description
+===========
+
+Get/set current transmit mode.
+
+Only :ref:`LIRC_MODE_PULSE <lirc-mode-pulse>` and
+:ref:`LIRC_MODE_SCANCODE <lirc-mode-scancode>` are supported by for IR send,
+depending on the driver. Use :ref:`lirc_get_features` to find out which
+modes the driver supports.
+
+Return Value
+============
+
+
+.. tabularcolumns:: |p{2.5cm}|p{15.0cm}|
+
+.. flat-table::
+    :header-rows:  0
+    :stub-columns: 0
+
+
+    -  .. row 1
+
+       -  ``ENODEV``
+
+       -  Device not available.
+
+    -  .. row 2
+
+       -  ``ENOTTY``
+
+       -  Device does not support transmitting.
+
+    -  .. row 3
+
+       -  ``EINVAL``
+
+       -  Invalid mode or invalid mode for this device.