omap: mailbox: reorganize headers

Remove kernel.h and module.h since they are not used correctly anyway.

Also, remove device.h since it comes along with platform_device.h
(always will I guess).

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Hiroshi DOYU <Hiroshi.DOYU@nokia.com>
diff --git a/arch/arm/plat-omap/mailbox.c b/arch/arm/plat-omap/mailbox.c
index fe08821..d2fafb8 100644
--- a/arch/arm/plat-omap/mailbox.c
+++ b/arch/arm/plat-omap/mailbox.c
@@ -21,10 +21,9 @@
  *
  */
 
-#include <linux/kernel.h>
-#include <linux/module.h>
 #include <linux/interrupt.h>
-#include <linux/device.h>
+#include <linux/spinlock.h>
+#include <linux/mutex.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/kfifo.h>