docs: add some directories to the main documentation index

The contents of those directories were orphaned at the documentation
body.

While those directories could likely be moved to be inside some guide,
I'm opting to just adding their indexes to the main one, removing the
:orphan: and adding the SPDX header.

For the drivers, the rationale is that the documentation contains
a mix of Kernelspace, uAPI and admin-guide. So, better to keep them on
separate directories, as we've be doing with similar subsystem-specific
docs that were not split yet.

For the others, well... I'm too lazy to do the move. Also, it
seems to make sense to keep at least some of those at the main
dir (like kbuild, for example). In any case, a latter patch
could do the move.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

Documentation/cdrom/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 =====
 cdrom

Documentation/fault-injection/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ===============
 fault-injection

Documentation/fb/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ============
 Frame Buffer

Documentation/fpga/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ====
 fpga

Documentation/ide/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ==================================
 Integrated Drive Electronics (IDE)

Documentation/index.rst

@@ -35,6 +35,7 @@ trying to get it to work optimally on a given system.
    :maxdepth: 2
 
    admin-guide/index
+   kbuild/index
 
 Firmware-related documentation
 ------------------------------
@@ -77,6 +78,9 @@ merged much easier.
    kernel-hacking/index
    trace/index
    maintainer/index
+   fault-injection/index
+   livepatch/index
+
 
 Kernel API documentation
 ------------------------
@@ -94,11 +98,20 @@ needed).
    core-api/index
    accounting/index
    block/index
+   cdrom/index
+   ide/index
+   fb/index
+   fpga/index
    hid/index
    iio/index
    leds/index
    media/index
+   netlabel/index
    networking/index
+   pcmcia/index
+   target/index
+   timers/index
+   watchdog/index
    input/index
    hwmon/index
    gpu/index

Documentation/kbuild/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ===================
 Kernel Build System

Documentation/livepatch/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ===================
 Kernel Livepatching

Documentation/netlabel/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ========
 NetLabel

Documentation/pcmcia/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ======
 pcmcia

Documentation/target/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ==================
 TCM Virtual Device

Documentation/timers/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ======
 timers

Documentation/watchdog/index.rst

-:orphan:
+.. SPDX-License-Identifier: GPL-2.0
 
 ======================
 Linux Watchdog Support