i2c: create builtin_i2c_driver to avoid registration boilerplate

In commit f309d4443130bf814e991f836e919dca22df37ae ("platform_device:
better support builtin boilerplate avoidance") we introduced the
builtin_driver macro.

Here we use that support and extend it to I2C driver registration,
so where a driver is clearly non-modular and builtin-only, we can
register it in a similar fashion.  And existing code that is clearly
non-modular can be updated with the simple mapping of

     module_i2c_driver(...)  ---> builtin_i2c_driver(...)

We've essentially cloned the former to make the latter, and taken
out the remove/module_exit parts since those never get used in a
non-modular build of the code.

A similar thing was done in commit b4eb6cdbbd13698704863f680c643c569909e1c2
("PCI: Add builtin_pci_driver() to avoid registration boilerplate").

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

include/linux/i2c.h

@@ -655,7 +655,7 @@ static inline int i2c_adapter_id(struct i2c_adapter *adap)
 }
 
 /**
- * module_i2c_driver() - Helper macro for registering a I2C driver
+ * module_i2c_driver() - Helper macro for registering a modular I2C driver
  * @__i2c_driver: i2c_driver struct
  *
  * Helper macro for I2C drivers which do not do anything special in module
@@ -666,6 +666,17 @@ static inline int i2c_adapter_id(struct i2c_adapter *adap)
 	module_driver(__i2c_driver, i2c_add_driver, \
 			i2c_del_driver)
 
+/**
+ * builtin_i2c_driver() - Helper macro for registering a builtin I2C driver
+ * @__i2c_driver: i2c_driver struct
+ *
+ * Helper macro for I2C drivers which do not do anything special in their
+ * init. This eliminates a lot of boilerplate. Each driver may only
+ * use this macro once, and calling it replaces device_initcall().
+ */
+#define builtin_i2c_driver(__i2c_driver) \
+	builtin_driver(__i2c_driver, i2c_add_driver)
+
 #endif /* I2C */
 
 #if IS_ENABLED(CONFIG_OF)