Don't use vdotq_s32 if it's not available (#139)
* Don't use vdotq_s32 if it's not available
`dotprod` extensions aren't available on some ARM CPUs (e.g. Raspberry Pi 4), so check for them and only use them if they're available.
Reintroduces the code removed in 84d9015 if `__ARM_FEATURE_DOTPROD` isn't defined.
* Update ggml.c
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
