* hexagon: add fp16 support for binary ops: add,sub,mul,div
* hexagon: fix test-backend-ops failures for fp16 binary ops on older arches (<v79)
* hexagon: decide on n_threads (aka n_jobs) early to avoid overallocating scratchpad
* snapdragon: fix readme link
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Co-authored-by: Max Krasnyansky <maxk@qti.qualcomm.com>
