Usage of Open MP Barrier for thread sync to avoid atomic operations

[abhishek-rn]

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Current ggml_compute thread requires exclusive sync operations for all the threads to sync after every stage of operation.
With recent introduction of openMP library into this repo, we can leverage the barrier function of openMP and also effectively remove atomic operations which introduces delay.

Command line:
./bin/llama-cli-m ../models/7B/ggml-model-q8_0.gguf -n 100 -s 01 -b 7 -t <num_of_threads> -p "AI is going to"
Running on Graviton 3 AWS machine with 64 cores

Threads	Master (tokens/sec)	PR Changes (tokens/sec)
4	6.2	6.19
8	11.75	11.7
16	20.94	20.95
24	23.97	25.03
32	25.7	27.46
48	26.26	29.71

We see improvements in tokens/sec by as much as ~3 token/sec over the existing implementation.
This is a small change in line with openMP library usage.
Request review and feedback.

[slaren]

It is already being done in #7993