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 <[email protected]> (v1)
Cc: Randy Dunlap <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Stephan Mueller <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: intel-gfx <[email protected]>
Cc: dri-devel <[email protected]>
Acked-by: Dave Airlie <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 9f935f5..27aa718 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -313,19 +313,15 @@
  *
  * Export callbacks:
  *
- *  - @gem_prime_pin (optional): prepare a GEM object for exporting
- *
- *  - @gem_prime_get_sg_table: provide a scatter/gather table of pinned pages
- *
- *  - @gem_prime_vmap: vmap a buffer exported by your driver
- *
- *  - @gem_prime_vunmap: vunmap a buffer exported by your driver
- *
- *  - @gem_prime_mmap (optional): mmap a buffer exported by your driver
+ *  * @gem_prime_pin (optional): prepare a GEM object for exporting
+ *  * @gem_prime_get_sg_table: provide a scatter/gather table of pinned pages
+ *  * @gem_prime_vmap: vmap a buffer exported by your driver
+ *  * @gem_prime_vunmap: vunmap a buffer exported by your driver
+ *  * @gem_prime_mmap (optional): mmap a buffer exported by your driver
  *
  * Import callback:
  *
- *  - @gem_prime_import_sg_table (import): produce a GEM object from another
+ *  * @gem_prime_import_sg_table (import): produce a GEM object from another
  *    driver's scatter/gather table
  */