drm: Extract drm_atomic_state_helper.[hc]

We already have a separate overview doc for this, makes sense to
untangle it from the overall atomic helpers.

v2: Rebase

v3: Rebase more.

Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181004202446.22905-4-daniel.vetter@ffwll.ch
diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
index f9cfcdcd..4b4dc23 100644
--- a/Documentation/gpu/drm-kms-helpers.rst
+++ b/Documentation/gpu/drm-kms-helpers.rst
@@ -59,12 +59,6 @@
 .. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
    :doc: implementing nonblocking commit
 
-Atomic State Reset and Initialization
--------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
-   :doc: atomic state reset and initialization
-
 Helper Functions Reference
 --------------------------
 
@@ -74,6 +68,21 @@
 .. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
    :export:
 
+Atomic State Reset and Initialization
+-------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_state_helper.c
+   :doc: atomic state reset and initialization
+
+Atomic State Helper Reference
+-----------------------------
+
+.. kernel-doc:: include/drm/drm_atomic_state_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_state_helper.c
+   :export:
+
 Simple KMS Helper Reference
 ===========================