[Kernel] Make rotary_embedding ops more flexible with input shape

[Isotr0py]

FIX #12729 (comment)

• Make rotary_embedding ops work with qk having shape of [seq_len, num_heads, head_dim]
• Clean up deepseek-v2/v3 and mla attention implementation

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[tlrmchlsmth]

Thanks for the fix! I think it would be best to add some TORCH_CHECKs so we don't hit another illegal memory access like you did when running DeepSeek 2VL, but otherwise looks good.