staging: tidspbridge: replace mbox callback with notifier_call

Lately, mailbox callbacks have been replaced by notifier block
call chains, this needs to be changed in the users of mailbox,
otherwise compilation will break due to missing parameters.

For this new change to work, io_mbox_msg needs to be compatible
with the notifier_call definition.

Reported-by: Hari Kanigeri <h-kanigeri2@ti.com>
Signed-off-by: Omar Ramirez Luna <omar.ramirez@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>