docs: update old references for DocBook from the documentation

a different interrupt, the driver will deadlock trying to recursively

acquire the spinlock.  Such deadlocks can be avoided by using

spin_lock_irqsave() or spin_lock_irq() which disable local interrupts

and acquire the lock (see Documentation/DocBook/kernel-locking).

and acquire the lock (see Documentation/kernel-hacking/locking.rst).

4.5 How to tell whether MSI/MSI-X is enabled on a device

   contains information about the problems, which may result by upgrading

   your kernel.

 - The Documentation/DocBook/ subdirectory contains several guides for

   kernel developers and users.  These guides can be rendered in a

   number of formats:  PostScript (.ps), PDF, HTML, & man-pages, among others.

   After installation, ``make psdocs``, ``make pdfdocs``, ``make htmldocs``,

   or ``make mandocs`` will render the documentation in the requested format.

Installing the kernel source

----------------------------

   sphinx.rst

   kernel-doc.rst

   parse-headers.rst

   docbook.rst

.. only::  subproject and html

kernel-doc comments have some special structure and formatting, but beyond that

they are also treated as reStructuredText.

There is also the deprecated DocBook toolchain to generate documentation from

DocBook XML template files under ``Documentation/DocBook``. The DocBook files

are to be converted to reStructuredText, and the toolchain is slated to be

removed.

Finally, there are thousands of plain text documentation files scattered around

``Documentation``. Some of these will likely be converted to reStructuredText

over time, but the bulk of them will remain in plain text.

FOURCC definitions are located in the linux/videodev2.h header. However, and

despite starting with the V4L2_PIX_FMT_prefix, they are not restricted to V4L2

and don't require usage of the V4L2 subsystem. FOURCC documentation is

available in Documentation/DocBook/v4l/pixfmt.xml.

available in Documentation/media/uapi/v4l/pixfmt.rst.

To select a format, applications set the grayscale field to the desired FOURCC.

For YUV formats, they should also select the appropriate colorspace by setting

the colorspace field to one of the colorspaces listed in linux/videodev2.h and

documented in Documentation/DocBook/v4l/colorspaces.xml.

documented in Documentation/media/uapi/v4l/colorspaces.rst.

The red, green, blue and transp fields are not used with the FOURCC-based API.

For forward compatibility reasons applications must zero those fields, and