Create device for Ethos-U kernel driver

When the Ethos-U kernel driver is probed it creates a /dev/ethosu<nr>
device node, which user space use ioctl to communicate with. When
the driver is removed the Ethos-U resources must live on until all
open file handles have been closed.

The rpmsg device can be removed for a number of reasons, for example
if the firmware is stopped or the remoteproc driver is removed. To
allow the remove to complete without waiting for all file handles to
close, a new 'struct device' is created by the kernel driver. This
device will be used to memory allocations and will live on until the
last file handle has been closed.

Change-Id: I790d8219960f25fe64f58c11a865eb65c7b08974
diff --git a/kernel/ethosu_device.h b/kernel/ethosu_device.h
index d02f29d..d866514 100644
--- a/kernel/ethosu_device.h
+++ b/kernel/ethosu_device.h
@@ -42,11 +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 ethosu_mailbox mailbox;
 };