Documentation: gpio: move sysfs into an obsolete section

The GPIO sysfs API is long obsolete, so highlight this even further
by moving it into an obsolete APIs section in both the admin-guide
and userspace-api books.

Signed-off-by: Kent Gibson <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

Documentation/admin-guide/gpio/index.rst

···
 
     Character Device Userspace API <../../userspace-api/gpio/chardev>
     gpio-aggregator
-    sysfs
     gpio-mockup
     gpio-sim
+    Obsolete APIs <obsolete>
 
 .. only::  subproject and html
 

Documentation/admin-guide/gpio/obsolete.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+Obsolete GPIO APIs
+==================
+
+.. toctree::
+    :maxdepth: 1
+
+    Sysfs Interface <../../userspace-api/gpio/sysfs>
+

Documentation/userspace-api/gpio/index.rst

···
     :maxdepth: 1
 
     Character Device Userspace API <chardev>
+    Obsolete Userspace APIs <obsolete>
 
 .. only::  subproject and html
 

Documentation/userspace-api/gpio/obsolete.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+Obsolete GPIO Userspace APIs
+============================
+
+.. toctree::
+    :maxdepth: 1
+
+    Sysfs Interface <sysfs>