[media] doc-rst: document LIRC_GET_LENGTH ioctl

Put documentation for this ioctl on its own page.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/uapi/rc/lirc-get-length.rst

+.. -*- coding: utf-8; mode: rst -*-
+
+.. _lirc_get_length:
+
+*********************
+ioctl LIRC_GET_LENGTH
+*********************
+
+Name
+====
+
+LIRC_GET_LENGTH - Retrieves the code length in bits.
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, __u32 *length )
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by open().
+
+``request``
+    LIRC_GET_LENGTH
+
+``length``
+    length, in bits
+
+
+Description
+===========
+
+Retrieves the code length in bits (only for ``LIRC-MODE-LIRCCODE``).
+Reads on the device must be done in blocks matching the bit count.
+The bit could should be rounded up so that it matches full bytes.
+
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.

Documentation/media/uapi/rc/lirc_device_interface.rst

@@ -18,4 +18,5 @@ LIRC Device Interface
     lirc-get-rec-resolution
     lirc-set-send-duty-cycle
     lirc-get-timeout
+    lirc-get-length
     lirc_ioctl

Documentation/media/uapi/rc/lirc_ioctl.rst

@@ -46,17 +46,6 @@ device can rely on working with the default settings initially.
 
 .. _lirc-request:
 
-I/O control requests
-====================
-
-.. _LIRC_GET_LENGTH:
-
-``LIRC_GET_LENGTH``
-
-    Retrieves the code length in bits (only for ``LIRC_MODE_LIRCCODE).``
-    Reads on the device must be done in blocks matching the bit count.
-    The bit could should be rounded up so that it matches full bytes.
-
 .. _LIRC_SET_SEND_MODE:
 .. _LIRC_SET_REC_MODE: