[POWERPC] Fix hardware IRQ time accounting problem.

The commit fa13a5a1 (sched: restore
deterministic CPU accounting on powerpc), unconditionally calls
update_process_tick() in system context.  In the deterministic
accounting case this is the correct thing to do.  However, in the
non-deterministic accounting case we need to not do this, since doing
this results in the time accounted as hardware irq time being
artificially elevated.

Also this collapses 2 consecutive '#ifdef CONFIG_VIRT_CPU_ACCOUNTING'
checks in time.h into one for neatness.
Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/process.c

@@ -350,7 +350,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	local_irq_save(flags);
 
 	account_system_vtime(current);
-	account_process_tick(current, 0);
+	account_process_vtime(current);
 	calculate_steal_time();
 
 	last = _switch(old_thread, new_thread);

include/asm-powerpc/time.h

@@ -237,18 +237,14 @@ struct cpu_usage {
 
 DECLARE_PER_CPU(struct cpu_usage, cpu_usage_array);
 
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
-extern void account_process_vtime(struct task_struct *tsk);
-#else
-#define account_process_vtime(tsk)		do { } while (0)
-#endif
-
 #if defined(CONFIG_VIRT_CPU_ACCOUNTING)
 extern void calculate_steal_time(void);
 extern void snapshot_timebases(void);
+#define account_process_vtime(tsk)		account_process_tick(tsk, 0)
 #else
 #define calculate_steal_time()			do { } while (0)
 #define snapshot_timebases()			do { } while (0)
+#define account_process_vtime(tsk)		do { } while (0)
 #endif
 
 extern void secondary_cpu_time_init(void);