[POWERPC] cell: add forward struct declarations to spu.h

Needed to be able to include spu.h independant from other
headers.
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

include/asm-powerpc/spu.h

@@ -161,6 +161,7 @@ struct spu_syscall_block {
 extern long spu_sys_callback(struct spu_syscall_block *s);
 
 /* syscalls implemented in spufs */
+struct file;
 extern struct spufs_calls {
 	asmlinkage long (*create_thread)(const char __user *name,
 					unsigned int flags, mode_t mode);
@@ -232,6 +233,7 @@ void spu_remove_sysdev_attr_group(struct attribute_group *attrs);
  * to object-id spufs file from user space and the notifer
  * function can assume that spu->ctx is valid.
  */
+struct notifier_block;
 int spu_switch_event_register(struct notifier_block * n);
 int spu_switch_event_unregister(struct notifier_block * n);