doc: update Kernel documentation build system

Update the documentation build system according to Linux v5.11-rc1.

Deactive the automarkup.py extension module which on Gitlab CI is
incompatible with Unicode.

With this patch we can build the HTML documentation using either of
Sphinx 2 and Sphinx 3.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

Revert "doc: update Kernel documentation build system"

Unfortunately we now see a number of now-fatal warnings about duplicate
labels. It is often unclear how best to re-write the document in
question to not duplicate these otherwise logical headings.

This reverts commit 10a1df3cd43ba2fe893d5dd1aeb2e7109ef0007f.

Signed-off-by: Tom Rini <trini@konsulko.com>

doc: update Kernel documentation build system

Update the docomentation build system according to Linux v5.11-rc1.

With this patch we can build the HTML documentation using either of
Sphinx 2 and Sphinx 3.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
[Fix warning in b4860qds.rst about "Switch Settings"]
Signed-off-by: Tom Rini <trini@konsulko.com>

doc: sphinx: refresh parse-headers.pl from Linux

Copy parse-headers.pl from Linux kernel tree:

* fix the parameter description %s/--man/--usage/
* fix a documentation reference

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

doc: Remove duplicated documentation directory

Commit ad7061ed742e ("doc: Move device tree bindings documentation to
doc/device-tree-bindings") moved all device tree binding documentation
to doc/device-tree-bindings directory.

The current U-Boot project still have two documentation directories:

- doc/
- Documentation/

Move all documentation and sphinx files to doc directory so all content
can be in a common place.

Signed-off-by: Breno Lima <breno.lima@nxp.com>

doc: sphinx: refresh parse-headers.pl from Linux

Copy parse-headers.pl from Linux kernel tree:

* fix the parameter description %s/--man/--usage/
* fix a documentation reference

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

doc: Remove duplicated documentation directory

Commit ad7061ed742e ("doc: Move device tree bindings documentation to
doc/device-tree-bindings") moved all device tree binding documentation
to doc/device-tree-bindings directory.

The current U-Boot project still have two documentation directories:

- doc/
- Documentation/

Move all documentation and sphinx files to doc directory so all content
can be in a common place.

Signed-off-by: Breno Lima <breno.lima@nxp.com>

doc: Remove duplicated documentation directory

Commit ad7061ed742e ("doc: Move device tree bindings documentation to
doc/device-tree-bindings") moved all device tree binding documentation
to doc/device-tree-bindings directory.

The current U-Boot project still have two documentation directories:

- doc/
- Documentation/

Move all documentation and sphinx files to doc directory so all content
can be in a common place.

Signed-off-by: Breno Lima <breno.lima@nxp.com>