[bugfix] fix apply_rotary_emb error on Ascend NPU

[FightingZhen]

What does this PR do?

When using Qwen2.5-VL model with Flash Attention 2, we find that the implementation logic about api torch_npu.npu_rotary_mul is a little bit different from the same api in package flash-attn.

The former can only accept input param x and sin/cos with 4-dimension and same attention head dimension, while the latter can accept param sin/cos with 2-dimension and attention head dimension chunked to half.

At the same time, we also find that the api apply_rotary_emb is also used in Qwen2.5-omni with the same situation as Qwen2.5-VL.

Therefore, this PR is committed for solving the above problem, and update flash attention judgement logic in Qwen2.5-omni and ems model from is_flash_attn_2_available to is_flash_attn_available at the same time.

Fixes # (issue)
#38189

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[Rocketknight1]

cc @SunMarc!

[SunMarc]

Thanks for fixing this ! There are still a few places where is_flash_attn_2_available is used instead of is_flash_attn_available that you introduced. Could you fix this ? Other than that LGTM !

[FightingZhen]

Thanks for fixing this ! There are still a few places where is_flash_attn_2_available is used instead of is_flash_attn_available that you introduced. Could you fix this ? Other than that LGTM !

@SunMarc Thanks for your suggestion, after rechecking the places where is_flash_attn_2_available is used, there are still some places where this func can not be replaced yet. Below are the places still need using is_flash_attn_2_available and corresponding reason:

1. Necessary ones: including the func in modeling_flash_attention_utils.py, modeling_utils.py and testing_utils.py, which are used for checking whether package flash-attn exists or not.
2. Still in progress ones: including the func in flash_paged.py and model modernbert. In order to make sure using them on Ascend NPU correctly, further experiments are still required. Once experimental results are confirmed, a new PR will be commited as soon as possible.
   2.1. The experiment about checking whether paged attention on Ascend NPU is ready or not;
   2.2. The experiment about developing corresponding implementation for the func apply_rotary implemented by triton in package flash-attn.

Additionally, this PR still requires some furthur self-tests, so we change it to draft for now. When it is ready, we will invite you for review, thanks!

[SunMarc]

Thanks for the update ! Please ping me when this is ready for review !

[FightingZhen]

@SunMarc We have finished self-testing the modifications in this PR, it is ready for review and merge :)

[SunMarc]

LGTM !

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