Use DMADirection type for dma_bdrv_io

Use DMADirection type for dma_bdrv_io

Currently dma_bdrv_io() takes a 'to_dev' boolean parameter to
determine the direction of DMA it is emulating.  We already have a
DMADirection enum designed specifically to encode DMA directions.
This patch uses it for dma_bdrv_io() as well.  This involves removing
the DMADirection definition from the #ifdef it was inside, but since that
only existed to protect the definition of dma_addr_t from places where
config.h is not included, there wasn't any reason for it to be there in
the first place.

Signed-off-by: David Gibson <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Reviewed-by: Andreas Färber <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>