Patch attention score far off issue for sd 1.5

[JingyaHuang]

What does this PR do?

Fixes #607

For the SD 1.5 checkpoint, we used to apply optimized attention score (replacing torch.badbmm by torch.bmm, since we don't have attention_mask as input, it could save some compute). But oddly, the trick works theoretically and works for other SD models, e.g. SD2, and SDXL, but not for SD 1.5...

We will apply in this PR a less optimized get_attention_scores for SD1.5 (almost the original one in diffusers) until we find the root cause.

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[dacorvo]

LGTM, thanks !