staging: most: dim2: use device to allocate coherent memory

On several architectures the allocation of coherent memory needs a device
that has the dma_ops structure properly initialized. This patch enables
the DIM2 platform to be used to allocate this type of memory.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>