drm: Split out drm_probe_helper.c from drm_crtc_helper.c

This is leftover stuff from my previous doc round which I kinda wanted
to do but didn't yet due to rebase hell.

The modeset helpers and the probing helpers a independent and e.g.
i915 uses the probing stuff but has its own modeset infrastructure. It
hence makes to split this up. While at it add a DOC: comment for the
probing libraray.

It would be rather neat to pull some of the DocBook documenting these
two helpers into in-line DOC: comments. But unfortunately kerneldoc
doesn't support markdown or something similar to make nice-looking
documentation, so the current state is better.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index 702c4474..677a025 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -2287,6 +2287,11 @@
 !Edrivers/gpu/drm/drm_crtc_helper.c
     </sect2>
     <sect2>
+      <title>Output Probing Helper Functions Reference</title>
+!Pdrivers/gpu/drm/drm_probe_helper.c output probing helper overview
+!Edrivers/gpu/drm/drm_probe_helper.c
+    </sect2>
+    <sect2>
       <title>fbdev Helper Functions Reference</title>
 !Pdrivers/gpu/drm/drm_fb_helper.c fbdev helpers
 !Edrivers/gpu/drm/drm_fb_helper.c