[POWERPC] fsl_soc: rtc-ds1307 support

Add support for the I2C devices handled by the rtc-ds1307 driver to
of_register_i2c_devices.

Cc: G. Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>