gallium: Add renderonly-based support for pl111+vc4.

gallium: Add renderonly-based support for pl111+vc4.

This follows the model of imx (display) and etnaviv (render): pl111 is a
display-only device, so when asked to do GL for it, we see if we have a
vc4 renderer, make the vc4 screen, and have vc4 call back to pl111 to do
scanout allocations.

The difference from etnaviv is that we share the same BO between vc4 and
pl111, rather than having a vc4 bo and a pl11 bo and copies between the
two.  The only mismatch between their requirements is that vc4 requires
4-pixel (at 32bpp) stride alignment, while pl111 requires that stride
match width.  The kernel will reject any modesets to an incorrect stride,
so the 3D driver doesn't need to worry about that.

v2: Rebase on Android rework, drop unused include.
v3: Fix another Android bug, from Rob Herring's build-testing.

Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>