radv: use dithered alpha-to-coverage

This matches the behaviour of AMDVLK and hides banding.
It is also seems to be allowed by the Vulkan spec.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
1 file changed