dtoc: Generate uclass devices

Add support for generating a file containing uclass instances. This avoids
the need to create these at run time.

Update a test uclass to include a 'priv_auto' member, to increase test
coverage.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/misc/test_drv.c b/drivers/misc/test_drv.c
index a2a77d3..f431a57 100644
--- a/drivers/misc/test_drv.c
+++ b/drivers/misc/test_drv.c
@@ -205,6 +205,7 @@
 	.name		= "testfdt",
 	.id		= UCLASS_TEST_FDT,
 	.flags		= DM_UC_FLAG_SEQ_ALIAS,
+	.priv_auto	= sizeof(struct dm_test_uc_priv),
 };
 
 static const struct udevice_id testfdtm_ids[] = {