util/bufferiszero: Remove useless prefetches

util/bufferiszero: Remove useless prefetches

Use of prefetching in bufferiszero.c is quite questionable:

- prefetches are issued just a few CPU cycles before the corresponding
  line would be hit by demand loads;

- they are done for simple access patterns, i.e. where hardware
  prefetchers can perform better;

- they compete for load ports in loops that should be limited by load
  port throughput rather than ALU throughput.

Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
Signed-off-by: Mikhail Romanov <mmromanov@ispras.ru>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240206204809.9859-5-amonakov@ispras.ru>