Sphinx supports generating Texinfo sources and Info documentation,
which can be navigated easily and is convenient to search (via the
indexed nodes or anchors, for example).  This is basically the same as
1f050e904dd6f2955eecbd22031d912ccb2e7683, which was recently applied
to the Linux kernel.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@savoirfairelinux.com>
Reviewed-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>