s390/idle: consolidate idle functions and definitions

Move the C functions and definitions related to the idle state handling
to arch/s390/include/asm/idle.h and arch/s390/kernel/idle.c. The function
s390_get_idle_time is renamed to arch_cpu_idle_time and vtime_stop_cpu to
enabled_wait.

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

arch/s390/include/asm/processor.h

@@ -289,7 +289,12 @@ static inline unsigned long __rewind_psw(psw_t psw, unsigned long ilc)
 	return (psw.addr - ilc) & mask;
 #endif
 }
- 
+
+/*
+ * Function to stop a processor until the next interrupt occurs
+ */
+void enabled_wait(void);
+
 /*
  * Function to drop a processor into disabled wait state
  */