opencl: allow loading precompiled binary kernels from library (llama/23042)

opencl: allow loading precompiled binary kernels from library (llama/23042)

* opencl: allow loading binary kernel

* opencl: add libdl.h

* ggml-backend-dl is in ggml, which depends backend libs, thus
  ggml-opencl cannot depend on ggml-backend-dl
* add libdl.h to break cyclic dep

* opencl: allow loading bin kernel lib

* opencl: load `gemm_moe_mxfp4_f32_ns` from kernel lib if available

* opencl: load q8_0 gemm from kernel lib

* opencl: load q4_0 moe gemm from kernel lib

* opencl: load q4_1 moe gemm from kernel lib

* opencl: load q4_k moe gemm from kernel lib

* opencl: always declare `get_adreno_bin_kernel_func_t`

* opencl: rephrase message

* opencl: fix for rebase

* opencl: update doc