staging/olpc_dcon: drop fb_notifier code

Previously we registered a notifier block to inform us of any framebuffer
device changes; if the screen was blanked or unblanked, we'd put the DCON
to sleep or wake it up.

Turns out that the backlight code registers a notifier block as well
and calls the update_status hook, so we can just use that to put the DCON
to sleep.  For those status updates where the blanking isn't changed,
dcon_sleep will do nothing.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>