model : add ASR support for LFM2-Audio-1.5B

[tdakhran]

LFM2-Audio-1.5B supports audio input and audio output.

PR adds only ASR support. To perform ASR invoke CLI with

bin/llama-mtmd-cli -m LFM2-Audio-1.5B-F32.gguf --mmproj mmproj-LFM2-Audio-1.5b-F32.gguf -n 30 --audio input.wav -sys "Perform ASR." -p "<__media__>"

Changes to existing code:

• model requires system prompt, -sys enabled for llama-mtmd-cli
• mel bins generation reworked, now it is generated dynamically and supports different n_fft values
• OP_SSM_CONV for CUDA backend is extended to support kernel size 9

cc: @ngxson

[tdakhran]

tested that llama-server works as intended with input

[
        {"role": "system", "content": "Perform ASR."},
        {
            "role": "user",
            "content": [
                {
                    "type": "input_audio",
                    "input_audio": {
                        "format": "wav",
                        "data": base64.b64encode(pathlib.Path("/data/playground/issue_400/10.wav").read_bytes()).decode(
                            "utf-8"
                        ),
                    },
                },
            ],
        },
    ]