[media] v4l: vb2-dma-contig: fail if user ptr buffer is not correctly aligned

The DMA transfer must be aligned to a specific value. If userptr is not aligned
to DMA requirements then unexpected corruptions of the memory may occur before
or after a buffer.  To prevent such situations, all unligned userptr buffers
are rejected at VIDIOC_QBUF.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>