anv, iris: Disable pre fetching the binding table entries on DG2

anv, iris: Disable pre fetching the binding table entries on DG2

On DG2 the HW will fetch the binding entries into the cache
for every single thread when a compute walker is dispatched,
wiping out the advantages of the cache prefetch.

The spec also advises to not do a cache prefetch when we have more than
31 binding table entries, but most real world applications will never
hit that limit.

Signed-off-by: Rohan Garg <rohan.garg@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18498>