[ARM] Add Cortex A7 support

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[ARM] generic: Add Sun7i SOC support

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[DOCS] Sun7i: add Cubieboard2 preliminary documentation.

This is not complete yet but it gives few hints.
In particular, how to get a PSCI enabled u-boot.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[DOCS] Sun7i: add intructions to allow autoboot of Xvisor.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>