doc-rst: migrate ioctl CEC_DQEVENT to c-domain

This is only one example, demonstrating the benefits of the patch
series.  The CEC_DQEVENT ioctl is migrated to the sphinx c-domain and
referred by ":name: CEC_DQEVENT".

With this change the indirection using ":ref:`CEC_DQEVENT` is no longer
needed, we can refer the ioctl directly with ":c:func:`CEC_DQEVENT`". As
addition in the index, there is a entry "CEC_DQEVENT (C function)".

Signed-off-by: Markus Heiser <markus.heiser@darmarIT.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/media/uapi/cec/cec-func-open.rst

@@ -32,7 +32,7 @@ Arguments
     Open flags. Access mode must be ``O_RDWR``.
 
     When the ``O_NONBLOCK`` flag is given, the
-    :ref:`CEC_RECEIVE <CEC_RECEIVE>` and :ref:`CEC_DQEVENT <CEC_DQEVENT>` ioctls
+    :ref:`CEC_RECEIVE <CEC_RECEIVE>` and :c:func:`CEC_DQEVENT` ioctls
     will return the ``EAGAIN`` error code when no message or event is available, and
     ioctls :ref:`CEC_TRANSMIT <CEC_TRANSMIT>`,
     :ref:`CEC_ADAP_S_PHYS_ADDR <CEC_ADAP_S_PHYS_ADDR>` and

Documentation/media/uapi/cec/cec-ioc-dqevent.rst

@@ -15,7 +15,8 @@ CEC_DQEVENT - Dequeue a CEC event
 Synopsis
 ========
 
-.. cpp:function:: int ioctl( int fd, int request, struct cec_event *argp )
+.. c:function:: int ioctl( int fd, int request, struct cec_event *argp )
+   :name: CEC_DQEVENT
 
 Arguments
 =========
@@ -36,7 +37,7 @@ Description
    and is currently only available as a staging kernel module.
 
 CEC devices can send asynchronous events. These can be retrieved by
-calling :ref:`ioctl CEC_DQEVENT <CEC_DQEVENT>`. If the file descriptor is in
+calling :c:func:`CEC_DQEVENT`. If the file descriptor is in
 non-blocking mode and no event is pending, then it will return -1 and
 set errno to the ``EAGAIN`` error code.