radv/winsys: set gart_page_size for null winsys

Fixes assertion failure when initializing memory types for devices without
dedicated vram.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33978>
1 file changed