tee: allow a driver to allocate a tee_device without a pool

A TEE driver doesn't always need to provide a pool if it doesn't
support memory sharing ioctls and can allocate memory for TEE
messages in another way. Although this is mentioned in the
documentation for tee_device_alloc(), it is not handled correctly.

Reviewed-by: Sumit Garg <[e-mail]>
Signed-off-by: Amirreza Zarrabi <[e-mail]>
Signed-off-by: Jens Wiklander <[e-mail]>

drivers/tee/tee_core.c

···
 
 	if (!teedesc || !teedesc->name || !teedesc->ops ||
 	    !teedesc->ops->get_version || !teedesc->ops->open ||
-	    !teedesc->ops->release || !pool)
+	    !teedesc->ops->release)
 		return ERR_PTR(-EINVAL);
 
 	teedev = kzalloc(sizeof(*teedev), GFP_KERNEL);