drm/i915: Separate intel_frontbuffer into its own header

In view of adding inline functions into the intel_frontbuffer section,
we first split the header into its own file so that we can integrate it
more easily with kerneldoc.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1470324762-2545-19-git-send-email-chris@chris-wilson.co.uk
diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst
index 2fe5952..87aaffc 100644
--- a/Documentation/gpu/i915.rst
+++ b/Documentation/gpu/i915.rst
@@ -70,6 +70,9 @@
 .. kernel-doc:: drivers/gpu/drm/i915/intel_frontbuffer.c
    :doc: frontbuffer tracking
 
+.. kernel-doc:: drivers/gpu/drm/i915/intel_frontbuffer.h
+   :internal:
+
 .. kernel-doc:: drivers/gpu/drm/i915/intel_frontbuffer.c
    :internal: