vmd: use the proper dma_* APIs instead of direct methods calls

With the bypass support for the direct mapping we might not always have
methods to call, so use the proper APIs instead.  The only downside is
that we will create two dma-debug entries for each mapping if
CONFIG_DMA_DEBUG is enabled.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Tested-by: Jesper Dangaard Brouer <brouer@redhat.com>
Tested-by: Tony Luck <tony.luck@intel.com>