ARM i.MX53: dts: add i2c aliases

This allows to order the i2c character devices correctly,
so that /dev/i2c-0 corresponds to i2c1, /dev/i2c-1 corresponds
to i2c2, and so on. Currently they are ordered by register
address.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>