s390: Add test case for RI

- Add new test "s390x_runtime_instr" to check if the RI control block is
   correctly restored when the RI is active.

 - Add RI control block in test s390x_regs_check.c

The original test case for RI has been provided by
Martin Schwidefsky <schwidefsky@de.ibm.com>

Signed-off-by: Alice Frosi <alice@linux.vnet.ibm.com>
Reviewed-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>