srcu: Debloat the <linux/rcu_segcblist.h> header

Linus noticed that the <linux/rcu_segcblist.h> has huge inline functions
which should not be inline at all.

As a first step in cleaning this up, move them all to kernel/rcu/ and
only keep an absolute minimum of data type defines in the header:

  before:   -rw-r--r-- 1 mingo mingo 22284 May  2 10:25 include/linux/rcu_segcblist.h
   after:   -rw-r--r-- 1 mingo mingo  3180 May  2 10:22 include/linux/rcu_segcblist.h

More can be done, such as uninlining the large functions, which inlining
is unjustified even if it's an RCU internal matter.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/srcutiny.c

@@ -30,6 +30,7 @@
 #include <linux/srcu.h>
 
 #include <linux/rcu_node_tree.h>
+#include "rcu_segcblist.h"
 #include "rcu.h"
 
 static int init_srcu_struct_fields(struct srcu_struct *sp)

kernel/rcu/srcutree.c

@@ -38,6 +38,7 @@
 #include <linux/srcu.h>
 
 #include "rcu.h"
+#include "rcu_segcblist.h"
 
 ulong exp_holdoff = 25 * 1000; /* Holdoff (ns) for auto-expediting. */
 module_param(exp_holdoff, ulong, 0444);

kernel/rcu/tree.h

@@ -30,9 +30,10 @@
 #include <linux/seqlock.h>
 #include <linux/swait.h>
 #include <linux/stop_machine.h>
-#include <linux/rcu_segcblist.h>
 #include <linux/rcu_node_tree.h>
 
+#include "rcu_segcblist.h"
+
 /*
  * Dynticks per-CPU state.
  */