CANN: Optimize CANN buffer pool memory management (llama/12875)

CANN: Optimize CANN buffer pool memory management (llama/12875)

Multiple optional memory pools are provided for CANN, including VMM,
priority queue-based, and traditional memory pools.
1.When the memory pool is available and GGML_CANN_DISABLE_VMM_POOL
   is not defined, the VMM pool is selected by default.
2.Otherwise, if GGML_CANN_ENABLE_BUF_PRIO_POOL is defined,
   the priority queue-based memory pool is used.
3.If neither condition is met, the default memory pool is used.