[VIDEO] add graphics and video

This MR adds video (weston, OpenGL and gstreamer video playback) support for QCS6490 and QCS615.

Loading the DTB from GRUB has been disabled to avoid overwriting the DTB provided by the firmware, which is loaded from dtb_a/dtb_b partitions and modified at runtime.

Known issue: in both platforms psplash crashes because the graphics driver is loaded later in the boot process and /dev/fb0 is not yet present when psplash tries to open it.

Signed-off-by: Alessandro Pecugi alessandro.pecugi@seco.com