etnaviv: Add support for KHR_partial_update
The damage region can be useful to optimize the "resolve" step that we have on imx6q (GC2000) because there isn't any tiling compatible with both render and scanout or an any GPU when scanning out a linear buffer since we don't support linear PE.
This improves fps for e.g weston-simple-egl
by factor 2 (~30 fps -> ~60 fps).