opencl : support k-quants (ggerganov#1836)

* Porting q2_k kernel to OpenCL

* Set global and local sizes for kernel calls for dequantizing k-quants

* Added q6_k kernel

* Fix q4_k opencl struct order

* Replace uchar with uint8_t

* Finish dequant kernels

* Added OpenCL DMMV kernels

* Fix q2_k, improve code

* Fix q3_k

* Shorten switch statements

* Improve code formatting

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Co-authored-by: Concedo <39025047+LostRuins@users.noreply.github.com>