Some more Q4_K and Q5_K speedup on CUDA (#2346)
* Faster Q5_K on CUDA
* Small Q5_K improvement on older GPUs
* Spped up Q4_K on CUDA
GTX1660: 29.5 ms/t -> 25.6 ms/t
RTX4080: 8.40 ms/t -> 8.25 ms/t
* Spped up Q4_K on CUDA
GTX1660: 36.7 ms/t -> 35.6 ms/t
RTX4080: 9.8 ms/t -> 9.5 ms/t
* Address PR comments
* Add some comments to satisfy PR reviewer
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Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>
