Fix Olimex A20 SOM configuration
Fix Olimex A20 SOM configuration

* Added missing kernel device tree definition.
* Updated U-Boot definiton.

(cherry picked from commit be22a388db6889177de039e5f1b98dd1b0d17865)

linux-sunxi/meta-sunxi,net147/meta-sunxi,twoerner/meta-sunxi,ebutera/meta-sunxi,linux-sunxi/meta-sunxi,soderstrom-rikard/meta-sunxi,linux-sunxi/meta-sunxi,soderstrom-rikard/meta-sunxi,geomatsi/meta-sunxi,net147/meta-sunxi,twoerner/meta-sunxi,ebutera/meta-sunxi,geomatsi/meta-sunxi