drm: Document drm_connector_funcs

drm: Document drm_connector_funcs

The special case here is that both ->detect and ->force are actually
functions only called by the probe helpers and hence really shouldn't
be here. But since they've used by pretty much every driver I figured
it's better to just document this for now instead of holding this doc
patch hostage until that's all fixed. For that reason also group force
right next to detect.

v2: Use FIXME comments to annotate where we should move a hook to
helpers.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449218769-16577-18-git-send-email-daniel.vetter@ffwll.ch
Reviewed-by: Thierry Reding <treding@nvidia.com>