i2c: create builtin_i2c_driver to avoid registration boilerplate

In commit f309d444 ("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 b4eb6cdb


("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>