anv: reduce working temporary memory for BVH builds

anv: reduce working temporary memory for BVH builds

Part of the memory allocated (private) is a temporary working buffer
for the GRL kernels. Once the build operation is done, the buffer
becomes unused.

Rather than allocate a new buffer each time, reuse the current last
allocated one if its size fits the next build operation.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25570>