mailbox startup and shutdown are being executed against
a single H/W module, and a mailbox H/W module is totally
__independent__ of the registration of logical mailboxes.
So, an independent mutext should be used for startup and
shutdown.
Signed-off-by: NFernando Guzman Lugo <x0095840@ti.com>
Signed-off-by: NHiroshi DOYU <Hiroshi.DOYU@nokia.com>