target-s390x: implement high-word facility

Besides RISBHG and RISBLG, all high-word instructions are not
implemented. Fix that.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Alexander Graf <agraf@suse.de>