srcu: Apply trivial callback lists to shrink Tiny SRCU

The rcu_segcblist structure provides quite a bit of functionality, and
Tiny SRCU needs almost none of it.  So this commit replaces Tiny SRCU's
uses of rcu_segcblist with a simple singly linked list with tail pointer.
This change significantly reduces Tiny SRCU's memory footprint, more
than making up for the growth caused by the creation of rcu_segcblist.c

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/init/Kconfig b/init/Kconfig
index d928a37..a2cfde1 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -573,7 +573,7 @@
 	  making these warnings mandatory for the tree variants.
 
 config RCU_NEED_SEGCBLIST
-	def_bool ( TREE_RCU || PREEMPT_RCU || TINY_SRCU || TREE_SRCU )
+	def_bool ( TREE_RCU || PREEMPT_RCU || TREE_SRCU )
 
 config CONTEXT_TRACKING
        bool