drm/doc: Convert to markdown

DRM Docbook is now Markdown ready. This means its doc is able to
use markdown text on it.

* Documentation/DocBook/drm.tmpl: Contains a table duplicated from
  drivers/gpu/drm/i915/i915_reg.h. This is not needed anymore

* drivers/gpu/drm/drm_modeset_lock.c: had a code example that used
  to look pretty bad on html. Fixed by using proper code markup.

* drivers/gpu/drm/drm_prime.c: Remove spaces between lines to make
  a proper markup list.

* drivers/gpu/drm/i915/i915_reg.h: Altought pandoc supports tables,
  it doesn't support table cell spanning. But we can use fixed-width
  for those special cases.

* include/drm/drm_vma_manager.h: Another code example that should be
  proper indented with four spaces.

v2 (Daniel): Adjust name to gpu.xml due to rename.

v3 (Daniel):
Split out the actual enabling in the Makefile - this way we can merge
the conversion, while just keeping the enabling in a drm-private tree.

Signed-off-by: Danilo Cesar Lemes de Paula <danilo.cesar@collabora.co.uk> (v1)
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephan Mueller <smueller@chronox.de>
Cc: Michal Marek <mmarek@suse.cz>
Cc: linux-kernel@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: intel-gfx <intel-gfx@lists.freedesktop.org>
Cc: dri-devel <dri-devel@lists.freedesktop.org>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448471279-19748-2-git-send-email-daniel.vetter@ffwll.ch
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 206b213..1dae5ac 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -855,31 +855,31 @@
  *
  * Note: DDI0 is digital port B, DD1 is digital port C, and DDI2 is
  * digital port D (CHV) or port A (BXT).
- */
-/*
- * Dual channel PHY (VLV/CHV/BXT)
- * ---------------------------------
- * |      CH0      |      CH1      |
- * |  CMN/PLL/REF  |  CMN/PLL/REF  |
- * |---------------|---------------| Display PHY
- * | PCS01 | PCS23 | PCS01 | PCS23 |
- * |-------|-------|-------|-------|
- * |TX0|TX1|TX2|TX3|TX0|TX1|TX2|TX3|
- * ---------------------------------
- * |     DDI0      |     DDI1      | DP/HDMI ports
- * ---------------------------------
  *
- * Single channel PHY (CHV/BXT)
- * -----------------
- * |      CH0      |
- * |  CMN/PLL/REF  |
- * |---------------| Display PHY
- * | PCS01 | PCS23 |
- * |-------|-------|
- * |TX0|TX1|TX2|TX3|
- * -----------------
- * |     DDI2      | DP/HDMI port
- * -----------------
+ *
+ *     Dual channel PHY (VLV/CHV/BXT)
+ *     ---------------------------------
+ *     |      CH0      |      CH1      |
+ *     |  CMN/PLL/REF  |  CMN/PLL/REF  |
+ *     |---------------|---------------| Display PHY
+ *     | PCS01 | PCS23 | PCS01 | PCS23 |
+ *     |-------|-------|-------|-------|
+ *     |TX0|TX1|TX2|TX3|TX0|TX1|TX2|TX3|
+ *     ---------------------------------
+ *     |     DDI0      |     DDI1      | DP/HDMI ports
+ *     ---------------------------------
+ *
+ *     Single channel PHY (CHV/BXT)
+ *     -----------------
+ *     |      CH0      |
+ *     |  CMN/PLL/REF  |
+ *     |---------------| Display PHY
+ *     | PCS01 | PCS23 |
+ *     |-------|-------|
+ *     |TX0|TX1|TX2|TX3|
+ *     -----------------
+ *     |     DDI2      | DP/HDMI port
+ *     -----------------
  */
 #define DPIO_DEVFN			0