gpu: host1x: Provide a proper struct bus_type

Previously the struct bus_type exported by the host1x infrastructure was
only a very basic skeleton. Turn that implementation into a more full-
fledged bus to support proper probe ordering and power management.

Note that the bus infrastructure needs to be available before any of the
drivers can be registered. This is automatically ensured if all drivers
are built as loadable modules (via symbol dependencies). If all drivers
are built-in there are no such guarantees and the link order determines
the initcall ordering. Adjust drivers/gpu/Makefile to make sure that the
host1x bus infrastructure is initialized prior to any of its users (only
drm/tegra currently).

v2: Fix building host1x and tegra-drm as modules
    Reported-by: Dave Airlie <airlied@gmail.com>

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Mark Zhang <markz@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/include/linux/host1x.h b/include/linux/host1x.h
index 7890b55..464f338 100644
--- a/include/linux/host1x.h
+++ b/include/linux/host1x.h
@@ -250,17 +250,29 @@
 struct host1x_device;
 
 struct host1x_driver {
+	struct device_driver driver;
+
 	const struct of_device_id *subdevs;
 	struct list_head list;
-	const char *name;
 
 	int (*probe)(struct host1x_device *device);
 	int (*remove)(struct host1x_device *device);
+	void (*shutdown)(struct host1x_device *device);
 };
 
-int host1x_driver_register(struct host1x_driver *driver);
+static inline struct host1x_driver *
+to_host1x_driver(struct device_driver *driver)
+{
+	return container_of(driver, struct host1x_driver, driver);
+}
+
+int host1x_driver_register_full(struct host1x_driver *driver,
+				struct module *owner);
 void host1x_driver_unregister(struct host1x_driver *driver);
 
+#define host1x_driver_register(driver) \
+	host1x_driver_register_full(driver, THIS_MODULE)
+
 struct host1x_device {
 	struct host1x_driver *driver;
 	struct list_head list;
@@ -273,7 +285,7 @@
 	struct mutex clients_lock;
 	struct list_head clients;
 
-	bool bound;
+	bool registered;
 };
 
 static inline struct host1x_device *to_host1x_device(struct device *dev)