drm/doc: Switch to sphinx/rst fixed-width quoting

Just fallout from switching from asciidoc to sphinx/rst.

v2: Found more. Also s/\//#/ in the vgpu ascii-art - sphinx treats
those as comments and switch to variable-width, which wreaks the
layout.

v3: Undo some of the hacks, rebasing onto latest version of Jani's
series fixed it.

Acked-by: Liviu Dudau <Liviu.Dudau@arm.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
diff --git a/drivers/gpu/drm/drm_vma_manager.c b/drivers/gpu/drm/drm_vma_manager.c
index 2f2ecde..f306c88 100644
--- a/drivers/gpu/drm/drm_vma_manager.c
+++ b/drivers/gpu/drm/drm_vma_manager.c
@@ -127,6 +127,9 @@
  * used to implement weakly referenced lookups using kref_get_unless_zero().
  *
  * Example:
+ *
+ * ::
+ *
  *     drm_vma_offset_lock_lookup(mgr);
  *     node = drm_vma_offset_lookup_locked(mgr);
  *     if (node)