Use a separate varaible to signal a "dead" controller (that has disappeared

Use a separate varaible to signal a "dead" controller (that has disappeared
from the bus, probably because of hot(un)plugging it).  This makes sure
that we still ack interrupts that arrive while the controller is "dying"
(when we go down into suspend or if an unrecoverable hardware error
occurs).  Fixes an interrupt storm when we suspend on Amlogic arm64 boards.

ok deraadt@