Replacing kmalloc/kfree/dma_map_single/dma_unmap_single() with
dma_alloc_coherent/dma_free_coherent() helps to reduce code size, and
simplify the code, and coherent DMA will not clear the cache every time.

The SOC that this driver supports does not have incoherent DMA, so this
makes the code follow the DMA API properly with no performance
impact. Currently there are missing dma sync calls around the DMA
transfers.

Link: https://lore.kernel.org/r/20210926061116.282-1-caihuoqing@baidu.comSigned-off-by: NCai Huoqing <caihuoqing@baidu.com>
Reviewed-by: NWenpeng Liang <liangwenpeng@huawei.com>
Tested-by: NWenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>