MINOR: tasks: extend the state bits from 8 to 16 and remove the reason

MINOR: tasks: extend the state bits from 8 to 16 and remove the reason

By removing the reason code for the wakeup we can gain 8 extra bits to
encode the task's state. The reason code was never used at all and is
wrong by design since subsequent calls will OR this value anyway. Let's
say it goodbye and leave the room for more precious bits. The woken bits
were moved to the higher byte so that the most important bits can stay
grouped together.