target/s390x: fix execution with icount

target/s390x: fix execution with icount

This patch adds some gen_io_start() calls to allow execution
of s390x targets in icount mode with -smp 1.
It enables deterministic timers and record/replay features.

Suggested-by: Richard Henderson <[email protected]>
Signed-off-by: Pavel Dovgalyuk <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Message-Id: <160455551747.32240.17074484658979970129.stgit@pasha-ThinkPad-X280>
Signed-off-by: Cornelia Huck <[email protected]>