staging/olpc_dcon: Add drm conversion to TODO

this driver is pretty horrible from a design pov, and needs a complete
overhaul. Concrete thing that annoys me is that it looks at
registered_fb, which is an internal thing to fbmem.c and fbcon.c. And
ofc it gets the lifetime rules all wrong (it should at least use
get/put_fb_info).

Looking at the history, there's been an attempt at dropping this from
staging in 2016, but that had to be reverted. Since then not real
effort except the usual stream of trivial patches, and fbdev has been
formally closed for any new hw support. Time to try again and drop
this?

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jens Frederich <jfrederich@gmail.com>
Cc: Daniel Drake <dsd@laptop.org>
Cc: Jon Nettleton <jon.nettleton@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-33-daniel.vetter@ffwll.ch