drm/kms-helpers: Extract drm_modeset_helper.[hc]

While reviewing docs I spotted that we have a few functions that
really just don't fit into their containing helper library section.
Extract them and shovel them all into a new library for random one-off
aux stuff.

v2: Remove wrongly added files for real.

Cc: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471034937-651-3-git-send-email-daniel.vetter@ffwll.ch
diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
index 34f755b..59fa3c1 100644
--- a/Documentation/gpu/drm-kms-helpers.rst
+++ b/Documentation/gpu/drm-kms-helpers.rst
@@ -258,3 +258,12 @@
 
 .. kernel-doc:: drivers/gpu/drm/drm_crtc.c
    :doc: Tile group
+
+Auxiliary Modeset Helpers
+=========================
+
+.. kernel-doc:: drivers/gpu/drm/drm_modeset_helper.c
+   :doc: aux kms helpers
+
+.. kernel-doc:: drivers/gpu/drm/drm_modeset_helper.c
+   :export: