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/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index e307725..482c109 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -886,7 +886,7 @@
  * PLLs can be routed to any transcoder A/B/C.
  *
  * Note: DDI0 is digital port B, DD1 is digital port C, and DDI2 is
- * digital port D (CHV) or port A (BXT).
+ * digital port D (CHV) or port A (BXT). ::
  *
  *
  *     Dual channel PHY (VLV/CHV/BXT)