package/mesa3d: add support for new virgl Gallium driver

http://cgit.freedesktop.org/mesa/mesa/commit/configure.ac?h=11.1&id=a8987b88ff1db4ac00720a9b56c4bc3aeb666537


"virgl is the 3D acceleration backend for the virtio-gpu shipping with
 qemu. The 3D acceleration is designed around gallium and TGSI as the
 virtualisation layer. The backend renderer translates the virgl
 interface into OpenGL currently."

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>