ARM: dts: i.MX51: Add i2c and spi aliases

This allows to order the i2c and spi devices correctly.
While at it reorder the aliases entries alphabetically.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>