sphinx: parser_yaml.py: fix line numbers information

sphinx: parser_yaml.py: fix line numbers information

As reported by Donald, this code:

	rst_parser = RSTParser()
	rst_parser.parse('\n'.join(result), document)

breaks line parsing. As an alternative, I tested a variant of it:

	rst_parser.parse(result, document)

but still line number was not preserved. As Donald noted,
standard Parser classes don't have a direct mechanism to preserve
line numbers from ViewList().

So, instead, let's use a mechanism similar to what we do already at
kerneldoc.py: call the statemachine mechanism directly there.

I double-checked when states and statemachine were introduced:
both were back in 2002. I also tested doc build with docutils 0.16
and 0.21.2. It worked with both, so it seems to be stable enough
for our needs.

Reported-by: Donald Hunter <donald.hunter@gmail.com>
Closes: https://lore.kernel.org/linux-doc/m24ivk78ng.fsf@gmail.com/T/#u
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>