etnaviv: fix FRONT_AND_BACK culling

HW has no value to cull both faces (setting both CW/CCW bits results in
only CCW being culled). The blob just skips triangle draws when FRONT_AND_BACK
culling is enabled. Lets do the same in draw_vbo(..).

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>

I rebased the original change from here flto/mesa@503e9619 and reworked it a little bit (use u_decomposed_prim(..) and update CI expectations).

Supersedes !3288 (closed)