Remove unnecessary includes of spinlock.h under include/linux

Remove the obviously unnecessary includes of <linux/spinlock.h> under the
include/linux/ directory, and fix the couple errors that are introduced as
a result of that.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index b72be2f..926adaa 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -1,7 +1,7 @@
 #ifndef __LINUX_PERCPU_H
 #define __LINUX_PERCPU_H
 
-#include <linux/spinlock.h> /* For preempt_disable() */
+#include <linux/preempt.h>
 #include <linux/slab.h> /* For kmalloc() */
 #include <linux/smp.h>
 #include <linux/string.h> /* For memset() */