hexagon: ssm-conv fix for large prompts (#23307)
* hexagon: remove gathers and better handling of vtcm in ssm-conv
* hexagon: relax ssm-conv gating requirements
* hexagon: add new prefill ssm-conv backend test
* hexagon: remove trailing white space
* hex-rope: uninline rope_cache_init, otherwise it breaks after rebaseing with SSM_CONV changes
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Co-authored-by: Max Krasnyansky <maxk@qti.qualcomm.com>
