S390: fix single stepped svcs with TRACE_IRQFLAGS=y

S390: fix single stepped svcs with TRACE_IRQFLAGS=y

commit 21ec7f6dbf10492ce9a21718040677d3e68bd57d upstream.

If irq flags tracing is enabled the TRACE_IRQS_ON macros expands to
a function call which clobbers registers %r0-%r5. The macro is used
in the code path for single stepped system calls. The argument
registers %r2-%r6 need to be restored from the stack before the system
call function is called.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>