docs: powerpc: convert vcpudispatch_stats.txt to ReST

- Add a SPDX header;
- Use standard markup for document title;
- Adjust identation on lists and add blank lines where
  needed;
- Add it to the powerpc index.rst file.

Acked-by: Michael Ellerman <mpe@ellerman.id.au> # powerpc
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/a88855cc8b3a97b9b918a33e78e9ad000cf64be1.1592203650.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>