staging: fsl-dpaa2/eth: Map Tx buffers as bidirectional

WRIOP hardware may need to write to the hardware annotation
area of Tx buffers (e.g. frame status bits) and also to
the data area (e.g. L4 checksum in frame header).

Map these buffers as DMA_BIDIRECTIONAL, otherwise the
write transaction through SMMU will not be allowed.

Signed-off-by: Nipun Gupta <nipun.gupta@nxp.com>
Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>