ARM: dts: mxs: Add ethernetX to macX aliases

Add ethernet0 and ethernet1 aliases into the imx28.dtsi file, as
that is what most bootloaders use to pass MAC address. The bootloader
seeks for this alias and adds "mac-address" and "local-mac-address"
properties to the aliased node. This fixes issues with FEC having
NULL MAC address when update_fec_mac_prop() wasn't called. And
not all boards call update_fec_mac_prop() .

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>