1. Introduce several new list/hash protecting mutexes, and access without any
mutex to several variables. The new mutexes are:
  - LRU_list_mutex for the LRU_list;
  - zip_free mutex for the zip_free arrays;
  - zip_hash mutex for the zip_hash hash and in_zip_hash flag;
  - free_list_mutex for the free_list and withdraw list;
  - flush_state_mutex for init_flush, n_flush, no_flush arrays.

2. The variables switched from buffer pool mutex protection to atomic operations
and/or os_rmb/os_wmb.
  - srv_buf_pool_old_size
  - srv_buf_pool_size
  - srv_buf_pool_curr_size
  - srv_buf_pool_base_size
  - buf_pool->buddy_stat[i].used
  - buf_pool->curr_size, n_chunks_new.

Reviewed-by: Debarun Banerjee <debarun.banerjee@oracle.com>
Reviewed-by: Allen Lai <zheng.lai@oracle.com>
RB: 9797