sycl: fix thread/block count in quantized cpy kernel launches (#27160)
Adjusts the thread/block count to be proportional to the size
of the quant, reducing under/over subscription.
Largest perf improvement is the q4_0 -> f32 path, with, on
a Arc 70, throughput goes from 20.21 GB/s to 158.19 GB/s
The rest of the quants are flat in performance uplift.