bit_spinlock: add required includes

Signed-off-by: NNick Piggin <npiggin@kernel.dk>

include/linux/bit_spinlock.h

 #ifndef __LINUX_BIT_SPINLOCK_H
 #define __LINUX_BIT_SPINLOCK_H
 
+#include <linux/kernel.h>
+#include <linux/preempt.h>
+#include <asm/atomic.h>
+
 /*
  *  bit-based spin_lock()
  *