move BLAS to a separate backend (#6210)

* move BLAS to a separate backend

* rename GGML_USE_OPENBLAS to GGML_USE_BLAS

* alloc : reuse same buffer when the same buffer type if used multiple times

* set number of threads automatically for openblas and blis

* sched : print assignments when GGML_SCHED_DEBUG env variable is set

* sched : allow ops with weights on an incompatible buffer type

This will cause the weight to be copied to a backend that supports the
op, which is very costly. The weight should have been stored in a buffer
of a backend that can run the op, but llama.cpp cannot do this
automatically at the moment.

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

examples/llama-bench/llama-bench.cpp

@@ -293,6 +293,7 @@ static cmd_params parse_cmd_params(int argc, char ** argv) {
     params.output_format = cmd_params_defaults.output_format;
     params.output_format_stderr = cmd_params_defaults.output_format_stderr;
     params.reps = cmd_params_defaults.reps;
+    params.numa = cmd_params_defaults.numa;
 
     for (int i = 1; i < argc; i++) {
         arg = argv[i];