scripts/kerneldoc: Switch to the Python kernel-doc script

scripts/kerneldoc: Switch to the Python kernel-doc script

Change the Sphinx config to run the new Python kernel-doc script
instead of the Perl one.  The only difference between the two is that
the new script does not handle the -sphinx-version option, instead
assuming that Sphinx is always at least version 3: so we must
delete the code that passes that option to avoid the Python
script complaining about an unknown option.

QEMU's minimum Sphinx version is already 3.4.3, so this doesn't
change the set of versions we can handle.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Message-id: 20250814171324.1614516-7-peter.maydell@linaro.org