Add the on-board rtc i2c device to the edb9307a platform init.

The EP93xx based EDB9307A dev board has an on-board ISL1208 RTC
connected to the I2C bus.  Now that the core code supports the
I2C bus, this patch will add support for the device.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>