ARM: OMAP: Allow I2C bus driver to be compiled as a module

Fixes a linker error when OMAP I2C bus driver is compiled as a module:

   ERROR: "i2c_register_board_info" [arch/arm/plat-omap/i2c.ko] undefined!

The I2C utility functions used for board initialization should be always
built-in.

Signed-off-by: Aaro Koskinen <Aaro.Koskinen@nokia.com>
Acked-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>