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

Documentation/gpu/drm-kms-helpers.rst

@@ -59,19 +59,28 @@ Implementing Asynchronous Atomic Commit
 .. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
    :doc: implementing nonblocking commit
 
+Helper Functions Reference
+--------------------------
+
+.. kernel-doc:: include/drm/drm_atomic_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
+   :export:
+
 Atomic State Reset and Initialization
 -------------------------------------
 
-.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_state_helper.c
    :doc: atomic state reset and initialization
 
-Helper Functions Reference
---------------------------
+Atomic State Helper Reference
+-----------------------------
 
-.. kernel-doc:: include/drm/drm_atomic_helper.h
+.. kernel-doc:: include/drm/drm_atomic_state_helper.h
    :internal:
 
-.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_state_helper.c
    :export:
 
 Simple KMS Helper Reference

drivers/gpu/drm/Makefile

@@ -36,7 +36,8 @@ drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
 		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
 		drm_kms_helper_common.o drm_dp_dual_mode_helper.o \
 		drm_simple_kms_helper.o drm_modeset_helper.o \
-		drm_scdc_helper.o drm_gem_framebuffer_helper.o
+		drm_scdc_helper.o drm_gem_framebuffer_helper.o \
+		drm_atomic_state_helper.o
 
 drm_kms_helper-$(CONFIG_DRM_PANEL_BRIDGE) += bridge/panel.o
 drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o