staging: olpc_dcon: clean up backlight handling

 - Move bl_val and bl_dev into dcon_priv struct....
 - The only time we ever read the backlight val from the dcon is
   at probe time.  Rather than calling dcon_get_backlight for that, just
   read from the register.
 - Drop dcon_get_backlight; it's just returning dcon->bl_val.
 - Rename dcon_set_backlight_hw to dcon_set_backlight, and drop the
   old dcon_set_backlight function.  Move contents of old dcon_set_backlight
   function into dconbl_set.
 - Shuffle backlight_ops callbacks around to be closer to struct, and
   rename them.
 - Make use of new backlight_properties arg to backlight_device_register,
   drop old code that set this manually.

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