We want to override the Sphinx theme only partially. So we need to
import the Sphinx theme.css. Cf.
https://docs.readthedocs.io/en/stable/guides/adding-custom-css.html

We also need to import the pygments.css for syntax highlighing.

Use sans-serif for body.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

Update theme_overrides.css from Linux v6.7.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

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>