radv: Refactor predication for compute queues.

radv: Refactor predication for compute queues.

Initialize the inverted predication VA only when it is used
for the first time.

This is needed to get conditional rendering work correctly with
task shaders because the internal compute cmdbuf may not exist
yet when conditional rendering starts.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16531>