i.mx6q: arm2: Add the enet function support

This enable the network function on the i.mx6q armadillo2
board(arm2), thus we can use tftp to load image from network.

Cc: Stefano Babic <sbabic@denx.de>
Signed-off-by: Jason Liu <jason.hui@linaro.org>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>