[S390] console_unblank woes.

The software watchdog calls machine_restart from a timer function.
The s390 machine_restart calls console_unblank to flush the console
output. This is needed for panic to get the panic message printed.
If console_unblank is called in interrupt a BUG is triggered in
acquire_console_sem. That makes the software watchdog panic instead
of restarting the machine. To get around this problem the call to
console_unblank is made conditionally on !in_interrupt() ||
oops_in_progress.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>