drm/sysfs: Send out uevent when connector->force changes

drm/sysfs: Send out uevent when connector->force changes

To avoid even more code duplication punt this all to the probe worker,
which needs some slight adjustment to also generate a uevent when the
status has changed to due connector->force.

v2: Instead of running the output_poll_work (which is kinda the wrong
thing and a layering violation since it's an internal of the probe
helpers), or calling ->detect (which is again a layering violation
since it's used only by probe helpers) just call the official
->fill_modes function, like a GET_CONNECTOR ioctl call.

v3: Restore the accidentally removed forced-probe for echo "detect" >
force.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447951610-12622-22-git-send-email-daniel.vetter@ffwll.ch
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>