docs: kernel_include.py: add support to generate a TOC table

docs: kernel_include.py: add support to generate a TOC table

When generate-cross-refs is used, instead of just implementing
the default of generating a literal block, we can also
generate a ReST file as a TOC.

The advantage is that, by being a ReST file, missing references
will point to the place inside the header file that has the
broken link.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/c0d32cd1ef94017e05984b0a38bd2516f7db21e2.1755872208.git.mchehab+huawei@kernel.org