um: virtio_uml: Fix broken device handling in time-travel

If a device implementation crashes, virtio_uml will mark it
as dead by calling virtio_break_device() and scheduling the
work that will remove it.

This still seems like the right thing to do, but it's done
directly while reading the message, and if time-travel is
used, this is in the time-travel handler, outside of the
normal Linux machinery. Therefore, we cannot acquire locks
or do normal "linux-y" things because e.g. lockdep will be
confused about the context.

Move handling this situation out of the read function and
into the actual IRQ handler and response handling instead,
so that in the case of time-travel we don't call it in the
wrong context.

Chances are the system will still crash immediately, since
the device implementation crashing may also cause the time-
travel controller to go down, but at least all of that now
happens without strange warnings from lockdep.

Fixes: c8177aba ("um: time-travel: rework interrupt handling in ext mode")
Cc: stable@vger.kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>