media: vivid: disable VB2_USERPTR if dma_contig was configured

It makes no sense to support the USERPTR memory model if the vivid instance was
configured as dma_contig. Disable it if this is the case.

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