* Update Q4_K and Q5_K to use branchless computation, which stops the scale unpack being re-executed for every column in mmvq, improving perf at batch sizes > 1
* Gating the change off from DGX Spark due to no gain
* Adding prefetch gated to Spark, making branchless change in Q4_K and Q5_K general and modifying switch points based on latest perf data
* Guard the mmvq L2 prefetch against MUSA as well as HIP
* Define the mmvq L2 prefetch only under the Spark guard
* Update switch point for Q4_K to accommodate more models
* Remove stale comments
* Add block_size to ggml_cuda_type_traits and create a separate mmvq_should_prefetch function
* Rename block_size to bs for cleaner indentation
* Fix build error on non-Spark CUDA arch with appropriate conditional around new function added
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Co-authored-by: praneshgo <227579474+praneshgo@users.noreply.github.com>
