docs: driver-api: properly format ToC headings

"class:: toc-title" was a workaround for older Sphinx versions that are
no longer supported.

The canonical way to add a heading to the ToC is to use :caption:.
Do that.

Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Armin Wolf <W_Armin@gmx.de>
Cc: Iwona Winiarska <iwona.winiarska@intel.com>
Cc: Ricardo Cañuelo <ricardo.canuelo@collabora.com>
Cc: Tomas Winkler <tomas.winkler@intel.com>
Cc: linux-media@vger.kernel.org
Cc: Yanteng Si <siyanteng@loongson.cn>
Cc: Alex Shi <alexs@kernel.org>
Cc: Wu XiangCheng <bobwxc@email.cn>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231027081830.195056-7-vegard.nossum@oracle.com

Documentation/driver-api/index.rst

@@ -9,11 +9,8 @@ of device drivers.  This document is an only somewhat organized collection
 of some of those interfaces — it will hopefully get better over time!  The
 available subsections can be seen below.
 
-.. class:: toc-title
-
-	   Table of contents
-
 .. toctree::
+   :caption: Table of contents
    :maxdepth: 2
 
    driver-model/index

Documentation/driver-api/media/index.rst

@@ -20,13 +20,8 @@ Documentation/userspace-api/media/index.rst
   - for the userspace APIs used on media devices.
 
 
-.. only:: html
-
-   .. class:: toc-title
-
-        Table of Contents
-
 .. toctree::
+    :caption: Table of Contents
     :maxdepth: 5
     :numbered:
 

Documentation/driver-api/mei/index.rst

@@ -9,13 +9,8 @@ Intel(R) Management Engine Interface (Intel(R) MEI)
 **Copyright** |copy| 2019 Intel Corporation
 
 
-.. only:: html
-
-   .. class:: toc-title
-
-        Table of Contents
-
 .. toctree::
+   :caption: Table of Contents
    :maxdepth: 3
 
    mei

Documentation/driver-api/pci/index.rst

@@ -4,11 +4,8 @@
 The Linux PCI driver implementer's API guide
 ============================================
 
-.. class:: toc-title
-
-	   Table of contents
-
 .. toctree::
+   :caption: Table of contents
    :maxdepth: 2
 
    pci

Documentation/translations/zh_CN/driver-api/gpio/index.rst

@@ -14,9 +14,8 @@
 通用型输入/输出（GPIO）
 =======================
 
-目录:
-
 .. toctree::
+   :caption: 目录
    :maxdepth: 2
 
    legacy

Documentation/translations/zh_CN/driver-api/index.rst

@@ -17,11 +17,8 @@ Linux驱动实现者的API指南
 内核提供了各种各样的接口来支持设备驱动的开发。这份文档只是对其中一些接口进行了
 一定程度的整理——希望随着时间的推移，它能变得更好！可用的小节可以在下面看到。
 
-.. class:: toc-title
-
-	   目录列表：
-
 .. toctree::
+   :caption: 目录列表
    :maxdepth: 2
 
    gpio/index