Some CPU, such as Xeon, can guarantee DMA cache coherency.
So it is no need to use dma sync APIs to flush cache on such CPUs.
In order to avoid calling dma sync APIs on the IO path, use the
dma_need_sync to check whether smc_buf_desc needs dma sync when
creating smc_buf_desc.
Signed-off-by: NGuangguan Wang <guangguan.wang@linux.alibaba.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>