Convert the i2c-sh_mobile i2c bus driver to use
subsys_initcall() instead of module_init().

This change makes the driver register a bit earlier which
together with earlier platform data moves the time for probe().
The earlier probe() makes it possible to use i2c_get_adapter()
and i2c_transfer() from device_initcall().

The same strategy is used by other i2c bus drivers such as
i2c-pxa.c and i2c-s3c2410.c.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>