sched/prio: Add 3 macros of MAX_NICE, MIN_NICE and NICE_WIDTH in prio.h

Currently there is lots of hard coding to 19 and -20, to represent
maximum and minimum of nice values.

This patch add three macros in prio.h for maximum, minimum and width
of nice value, and uses it to remove hardcoded values in prio.h.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/3994e89327b2b15f992277cdf9f409c516f87d1b.1392103744.git.yangds.fnst@cn.fujitsu.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[ Collapsed two small patches. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched/prio.h

@@ -1,6 +1,10 @@
 #ifndef _SCHED_PRIO_H
 #define _SCHED_PRIO_H
 
+#define MAX_NICE	19
+#define MIN_NICE	-20
+#define NICE_WIDTH	(MAX_NICE - MIN_NICE + 1)
+
 /*
  * Priority of a process goes from 0..MAX_PRIO-1, valid RT
  * priority is 0..MAX_RT_PRIO-1, and SCHED_NORMAL/SCHED_BATCH
@@ -17,8 +21,8 @@
 #define MAX_USER_RT_PRIO	100
 #define MAX_RT_PRIO		MAX_USER_RT_PRIO
 
-#define MAX_PRIO		(MAX_RT_PRIO + 40)
-#define DEFAULT_PRIO		(MAX_RT_PRIO + 20)
+#define MAX_PRIO		(MAX_RT_PRIO + NICE_WIDTH)
+#define DEFAULT_PRIO		(MAX_RT_PRIO + NICE_WIDTH / 2)
 
 /*
  * Convert user-nice values [ -20 ... 0 ... 19 ]