dt: Add default match table for bus ids

No need for most platforms to define their own bus table when calling
of_platform_populate().  Supply a stock one.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/of_platform.h

@@ -40,6 +40,8 @@ struct of_platform_driver
 #define	to_of_platform_driver(drv) \
 	container_of(drv,struct of_platform_driver, driver)
 
+extern const struct of_device_id of_default_bus_match_table[];
+
 /* Platform drivers register/unregister */
 extern struct platform_device *of_device_alloc(struct device_node *np,
 					 const char *bus_id,