anv: flush tile cache between steps of AS builds
The GRL metakernel kernels are partly implemented using the command streamer. We need to flush the tile cache + cs stall to ensure shader writes are visible by CS.
Signed-off-by: Lionel Landwerlin lionel.g.landwerlin@intel.com Fixes: f3ddfd81 ("anv: Build BVHs on the GPU with GRL")