Hexagon (target/hexagon) Short-circuit packet predicate writes

Hexagon (target/hexagon) Short-circuit packet predicate writes

In certain cases, we can avoid the overhead of writing to hex_new_pred_value
and write directly to hex_pred.  We consider predicate reads/writes when
computing ctx->need_commit.  The get_result_pred() function uses this
field to decide between hex_new_pred_value and hex_pred.  Then, we can
early-exit from gen_pred_writes.

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230427230012.3800327-13-tsimpson@quicinc.com>