media: staging/imx: Pass device to alloc/free_dma_buf

Allocate and free a DMA coherent buffer in imx_media_alloc/free_dma_buf()
from the given device. This allows DMA alloc and free using a device
that is backed by real hardware, which for the imx5/6/7 CSI is the CSI
unit, and for the internal IPU sub-devices, is the parent IPU.

Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>