staging: olpc_dcon: change sysfs 'output' toggle to be clearer...

..and store it in dcon_priv.  This renames it to 'monochrome',
which I think is much clearer.  Previously, "echo 1 > output"
toggled mono mode, while "echo 0 > output" enabled color.
"Echo 1 > monochrome" makes more sense to me.

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