mlx5: Make MLX5_COMP_EQ_SIZE tunable.

When using hardware pacing, this value can be increased, because more SQ's
means more EQ events aswell. Make it tunable, hw.mlx5.comp_eq_size .

Sponsored by: NVIDIA Networking

(cherry picked from commit 3bb3e4768ff854b88ba0a7d129edad49f15d7ce3)