board/via/imx6_vab820: update to latest BSP release

Changes:
* Update Kernel and U-Boot to the latest 2.0.6 BSP release from the
official sources.
* Add genimage config to create bootable SD card image

Signed-off-by: Gergely Imreh <imrehg@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>