ARM: imx: Add initial support for Freescale LS1021A

The LS1021A SoC is a dual-core Cortex-A7 based processor,
this adds the initial support for it.

Signed-off-by: Jingchang Lu <b35083@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>