arm/imx6q: Rename Sabreauto to Armadillo2

The Sabreauto board was renamed to Armadillo2 recently. To avoid
confusion, rename Sabreauto to Armadillo2/arm2.

Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>