drm/mcde: Fix Sphinx formatting

- Format the pipe diagram as a monospace block.
- Fix formatting of the list. Without the empty line, the first dash is
  not parsed as a bullet point.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200214163815.25442-1-j.neuschaefer@gmx.net