python3-sphinx: upgrade 7.0.1 -> 7.1.1

python3-sphinx: upgrade 7.0.1 -> 7.1.1

No longer need to set PYPI_PACKAGE, download is
now sphinx-${PV}.tar.gz not Sphinx-${PV}.tar.gz.

https://www.sphinx-doc.org/en/master/changes.html#release-7-1-1-released-jul-27-2023
https://www.sphinx-doc.org/en/master/changes.html#release-7-1-0-released-jul-24-2023

Signed-off-by: Tim Orling <tim.orling@konsulko.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>