fio: fix s390 time accounting

The current timer implementation could cause time warps on s390 which ends up
as time bound jobs that would never end, because they always reset themself to
the old time.

When touching this code anyway, we also change it to use the faster stckf
and avoid the calibration as we can control the result to be usecs.
This also eliminates a few calculations cycle->usec in the hot path for the
timer.

In case other architectures have similar improved timers that might not be
usec based, but nsec based or such a thing any architecture can set
ARCH_CPU_CLOCK_CYCLES_PER_USEC to an appropriate per-arch value.
This leaves the infrastructure open for others and the compiler will throw
our division by 1 away anyway.

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
fio: fix s390 nop

When trying to run rate limited fio runs we encountered that the current
definition of a nop uses a privileged instruction which is not even a nop,
but a yield call to the hipervisor.
That leads to a SIGILL as it is privileged.

To solve that issue replace it with a nop, the assembler will take care
of it (likely to become a BCR 0,0)

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <axboe@fb.com>