fix torchair execute issue on padding data, and mtp padding logic (vllm-project#1160)

The former PR vllm-project#736
select the valid token inside the `input_ids` and `position_ids` breaks
the necessary padding required by torchair. In this PR, we pending the
pad logic after the multimodal part.

Signed-off-by: ganyi <pleaplusone.gy@gmail.com>

Author: ganyi1996ppo