s390x: translate engine for s390x CPU

This is the main meat part of the patch set. It implements emulation for an
s390x CPU.

The code does all the optimizations that are common for TCG code:

 - direct branches
 - cc optimization
 - unrolling of simple microcode loops

I'm still open for suggestions on speedups of course :).
Signed-off-by: NAlexander Graf <agraf@suse.de>