Add DRI-based generic backend

Add DRI-based generic backend

mesa3d project support graphic buffer allocation via DRI API for
various set of hardware, including systems with splitted GPU
and Display controller.

Use it as fallback backend in case no other backends were found in
the supported list.

Tested with Android on sun4i-drm and lima GPU (Pinephone).

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
Change-Id: I9d6ed0bdf3ef255c3c4f9be5385a7b87b571a232