staging/olpc_dcon: move wait queue into dcon_priv struct

Another global variable (dcon_wait_queue) moved into the dcon_priv struct.
In the process, replace an instance of a manually implemented
wait_event_timeout.  This code came from Jordan's original gxfb_dcon.c
driver waaaay back in 2006; well past time for a replacement.

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