Break circulare dependency on struct ethosu_device

The 'struct ethosu_device' has been passed as argument to classes.
This creates a circular dependency dependency and it gives all
classes full visibility to all resources in the device struct. This
patch removes the circular dependency.

Using device_lock() and device_unlock() to for synchronization.

Change-Id: I8322e6530c72d7bd67f48f411b4f14b612be2706
diff --git a/kernel/ethosu_device.h b/kernel/ethosu_device.h
index cc4271d..d02f29d 100644
--- a/kernel/ethosu_device.h
+++ b/kernel/ethosu_device.h
@@ -42,13 +42,11 @@
  * struct ethosu_device - Device structure
  */
 struct ethosu_device {
-	struct device         *dev;
 	struct rpmsg_device   *rpdev;
 	struct rpmsg_endpoint *ept;
 	struct cdev           cdev;
 	struct                class *class;
 	dev_t                 devt;
-	struct mutex          mutex;
 	struct ethosu_mailbox mailbox;
 };
 
@@ -61,14 +59,13 @@
  *
  * Return: 0 on success, else error code.
  */
-int ethosu_dev_init(struct ethosu_device *edev,
-		    struct rpmsg_device *rpdev,
+int ethosu_dev_init(struct rpmsg_device *rpdev,
 		    struct class *class,
 		    dev_t devt);
 
 /**
  * ethosu_dev_deinit() - Initialize the device
  */
-void ethosu_dev_deinit(struct ethosu_device *edev);
+void ethosu_dev_deinit(struct rpmsg_device *rpdev);
 
 #endif /* ETHOSU_DEVICE_H */