[S390] improve irq tracing code in entry[64].S

The system call path in entry[64].S is run with interrupts enabled.
Remove the irq tracing check from the system call exit code. If a
program check interrupted a context enabled for interrupts do a
call to trace_irq_off_caller in the program check handler before
branching to the system call exit code.
Restructure the system call and io interrupt return code to avoid
avoid the lpsw[e] to disable machine checks.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/system.h

@@ -459,11 +459,6 @@ extern void (*_machine_power_off)(void);
 
 #define arch_align_stack(x) (x)
 
-#ifdef CONFIG_TRACE_IRQFLAGS
-extern psw_t sysc_restore_trace_psw;
-extern psw_t io_restore_trace_psw;
-#endif
-
 static inline int tprot(unsigned long addr)
 {
 	int rc = -EFAULT;