of/platform: remove all of_bus_type and of_platform_bus_type references

Both of_bus_type and of_platform_bus_type are just #define aliases
for the platform bus.  This patch removes all references to them and
switches to the of_register_platform_driver()/of_unregister_platform_driver()
API for registering.

Subsequent patches will convert each user of of_register_platform_driver()
into plain platform_drivers without the of_platform_driver shim.  At which
point the of_register_platform_driver()/of_unregister_platform_driver()
functions can be removed.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/serial/sunsu.c b/drivers/serial/sunsu.c
index 5deafc8..3cdf748 100644
--- a/drivers/serial/sunsu.c
+++ b/drivers/serial/sunsu.c
@@ -1586,7 +1586,7 @@
 			return err;
 	}
 
-	err = of_register_driver(&su_driver, &of_bus_type);
+	err = of_register_platform_driver(&su_driver);
 	if (err && num_uart)
 		sunserial_unregister_minors(&sunsu_reg, num_uart);