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>
